This character is mainly made for heavy crossbow and maybe some other back up weapons. This character is suppose top be a hit-man of sort to sum up the story of this guy. My issue is, how do i level this up? My current hope is to multiclass Fighter/Rogue though mainly Rogue for scaling up sneak attack.  If you have tips on how to play this character i'll be grateful! 

Few Notes:

All official races are allowed and 27 points system.

Are there feats, how do backgrounds work in this campaign?

Either way, start with the following ability scores: 10 STR, 15 DEX, 14 CON, 10 INT, 11 WIS, 12 CHA.

I suggest starting as Rogue and selecting Half-Elf as your Race. Your CHA is now 14, put the two variable ability score increases in DEX (now 16) and WIS (now 12). You have four Skills you gain Proficiencies in for Rogue, select Stealth, Intimidation, Deception, and Perception. You have two Skills you gain Proficiencies in for Half-Elf, select Acrobatics and Athletics. These skill selections may change based on how backgrounds work, but if you have custom backgrounds select Insight and Sleight of Hand for the Skills, and Disguise Kit and Poisoner's Kit for the Tools (unless your going Assassin Archetype then select Racial Languages). Put your second level in Fighter and select Archery as your Fighting Style. Then get to third level of Rouge and select your Roguish Archetype. Then get to third level of Fighter and select Champion as your Archetype. Then every level thereafter should be Rogue. Focus on Dexterity, your Crossbow, and Finesse Weapons.

That's my build advice. I might try RP advice latter.

Yes, Most likely. I know my DMs and they never minded them. Though they hate homebrew/UA stuff so they are out of the option list. Also i forgot to mention, Probably if going 3 levels fighter will take battlemaster and rogue will defiantly be assassin as you said.

I usually don't suggest selecting Battlemaster unless Fighter is your primary Class, because you won't get as many Maneuver uses out of it. However since you can get Feats after you hit 20 DEX you could pick up Combat Initiate to get more uses. I will change my suggestions to match.

With Rogue 17/Fighter 3 you get 5 Attribute Increasements, the first 2 will get you to 20 DEX, giving you 3 Feats. I would suggest Combat Initiate, Sharpshooter, and Lucky. You might be wondering why I didn't say Crossbow Expert, that's because it's only really useful if your either using a Hand Crossbow, or have Extra Attack. Though if you still want to have your Bonus Action free after Attacking, pick it up at the expense of one of the other Feats.

Quote from SladeTracey >>

Are there feats, how do backgrounds work in this campaign?

Either way, start with the following ability scores: 10 STR, 15 DEX, 14 CON, 10 INT, 11 WIS, 12 CHA.

I suggest starting as Rogue and selecting Half-Elf as your Race. Your CHA is now 14, put the two variable ability score increases in DEX (now 16) and WIS (now 12). You have four Skills you gain Proficiencies in for Rogue, select Stealth, Intimidation, Deception, and Perception. You have two Skills you gain Proficiencies in for Half-Elf, select Acrobatics and Athletics. These skill selections may change based on how backgrounds work, but if you have custom backgrounds select Insight and Sleight of Hand for the Skills, and Disguise Kit and Poisoner's Kit for the Tools (unless your going Assassin Archetype then select Racial Languages). Put your second level in Fighter and select Archery as your Fighting Style. Then get to third level of Rouge and select your Roguish Archetype. Then get to third level of Fighter and select Champion as your Archetype. Then every level thereafter should be Rogue. Focus on Dexterity, your Crossbow, and Finesse Weapons.

That's my build advice. I might try RP advice latter.

And FWIW, I really like this because it's optimized without being meta and power-gamey. All of those decisions make sense internally to the game too. (I mean, maybe 'champion' is a bit mis-named for this character, but the theme of the arch fits. You're just a 'champion' of killing :)

Thanks, it's the kind of characters I usually build, I focus more on perfecting an idea. I really like finding ways to make interesting builds also good builds. Basically every character I've made has a gimmick, which is why I have a hard time playing Bards.

Quote from SladeTracey >>

I usually don't suggest selecting Battlemaster unless Fighter is your primary Class, because you won't get as many Maneuver uses out of it. However since you can get Feats after you hit 20 DEX you could pick up Combat Initiate to get more uses. I will change my suggestions to match.

With Rogue 17/Fighter 3 you get 5 Attribute Increasements, the first 2 will get you to 20 DEX, giving you 3 Feats. I would suggest Combat Initiate, Sharpshooter, and Lucky. You might be wondering why I didn't say Crossbow Expert, that's because it's only really useful if your either using a Hand Crossbow, or have Extra Attack. Though if you still want to have your Bonus Action free after Attacking, pick it up at the expense of one of the other Feats.

 Tbh, i only took Battlemaster because it's the best of them since i get a D8 extra with some effects such as precise strike ( i am a shitty roller so this might help out if i went with sharpshooter feature), the intimidate one for extra damage and maybe fear, and finally either disarm or trip kinda situational but they are extra damage as well. 

Though Champion has it's tempt with crit on 19 but a big gamble on a guy who rolls mostly low (mostly 1 tbh with different sets...) Still i really loved your dice and to my luck there is potentially a one shot tomorrow and might give it a try! Wish me luck. 

A sniper concept is one of the few times I might take arcane archer for the fighter subclass. That subclass is based around having 2 really good shots per short rest. Sounds about like a sniper to me.

One thing about Arcane Archer: "Once per turn when you fire an arrow from a shortbow or longbow as part of the Attack action, you can apply one of your Arcane Shot options to that arrow"

Technically not crossbows, but may work if the DM is willing to apply to crossbows too. (seeking arrow is a nice way to hit people around corners)

Although Assassin kinda fits the hitman theme, you might also want to consider Inquisitive subclass. Sneak attack on every shot after a successful insight check regardless of whether there's an enemy of your target within 5ft. (also sneak attack damage increases by 3d6 at lvl 17) Still fits into a hitman, but one that watches their targets, finding the points at which they're vulnerable and striking then. (Issue with assassin is it relies on surprising the enemy AND being before them in initiative order to be fully effective.)

Going for a rogue sniper build I'd drop the CON 14 down and put the points into INT/WIS/CHA depending on which skills/tools you want to be better at.

Feats: Sharpshooter is always a good one for ranged characters, skulker could also be useful (can hide when lightly obscured, if you miss you stay hidden), Lucky (3 rerolls/long rest can always be useful), keen mind (for more an RP feat, you are expert at planning your kills and can remember every detail about the plan), Elven Accuracy (advantage becomes 3 dice instead of 2), Alert (if you're going assassin the +5 to initiative could be useful to get that 1st round advantage)

Races: Elf (+2 DEX, Darkvision, Elven accuracy feat), Rock Gnome (+1 DEX, 120ft Darkvision, advantage on stealth in rocky terrain), Lightfoot Halfling (+2 DEX, Lucky (reroll 1s), can hide behind medium creatures), Variant human (+1 DEX, feat at 1st level), Aarakocra (+2 DEX, can fly), Bugbear (if allowed, +1 DEX, darkvision, +5ft reach with melee weapons, High carry capacity, +2d6 damage on 1st hit against surprised enemy), Kenku (+2 DEX, forgery, mimicry), Kobold (if allowed but watch out for sunlight sensitivity, +2 DEX, darkvision, pack tactics), Tabaxi (+2 DEX, darkvision, bursts of speed), Feral Tiefling (+2 DEX, darkvision, fire resistance, spells/flying), Changeling (+1 DEX, change appearance), Skirmisher warforged (+2 DEX, faster movement, high resilience, don't need to eat, rest, breathe, or drink, AC = 11+prof mod+DEX mod)

I'd lean towards changeling (if rp to blend in before you kill people), Elf (darkvision, elven accuracy, wood elf for movement and hiding, for combat ability), Skirmisher Warforged (good all round, and cool as an unstoppable hitman)

Fighter subclass I'd also lean towards champion, but arcane archer (if allowed to work with crossbows) could give some interesting shots, and Samurai's fighting spirit (for 3x turns of attacking with advantage/long rest) along with lucky with an extra dice per advantage with elven accuracy could do well to optimise crits or at least high rolls (although it doesn't fit thematically as well as the others {Champion of killing, master of the perfect shot (Arcane archer)}).

If you don't go assassin, I'd recommend trying to get prof with poisoner's kit for some extra methods of killing/subduing enemies.

I was intrigued by this ideas, but I red that sneak attack can only be done once per turn. Does the inquisitive ability over ride that?

Sneak attack can occur once per turn. So once on your turn and then once more on an enemies turn if you can use your reaction to attack. (up to 2 times per round)

Inquistive's ability Insightful Fighting only gives you another way to cause sneak attack, not an additional use of it. (swashbuckler has a similar ability)

The Scout subclass allows you to make 2 attacks on your turn and use sneak attack on both as long as they are against different targets (lvl 17 ability) (this can give a total of 3 sneak attacks per round)

Hobgoblin's gain proficiency with two martial weapons of your choice. You can pick Heavy Crossbow as one, then go straight Rogue without dipping into fighter at all. As a Rogue you wont get that extra attack, thus you won't have to choose between SS or CBE, but your damage output will still be really good. Plus Saving Face is really good if you are taking the -5 to deal more damage.

Personally I'd go Inquisitive for insightful fighting and flavor yourself as a Bounty Hunter. Inquisitive can be a bit MAD, but since you don't have to dip you can boost you attributes more often.

Also, if you don't want to be a Hobgoblin ask your DM if you can reskin it as a human, I don't know why they would say no.

Quote from Whiskeyjack8044 >>

Hobgoblin's gain proficiency with two martial weapons of your choice. You can pick Heavy Crossbow as one, then go straight Rogue without dipping into fighter at all. As a Rogue you wont get that extra attack, thus you won't have to choose between SS or CBE, but your damage output will still be really good. Plus Saving Face is really good if you are taking the -5 to deal more damage.

Personally I'd go Inquisitive for insightful fighting and flavor yourself as a Bounty Hunter. Inquisitive can be a bit MAD, but since you don't have to dip you can boost you attributes more often.

Also, if you don't want to be a Hobgoblin ask your DM if you can reskin it as a human, I don't know why they would say no.

 The only reason i decided to multiclass into fighter is to gain the archery fighting style and some extra effects (though might neglect it) from battlemaster as extra flavor.

Barbarian Path of the Ancestral Guardians + Rogue Mastermind for maximum shenanigans.