Hey guys. At the start of my next campaign, I intend to make my players start off as standard commoners, who will discover their classes via the actions they take in the first two/three sessions (i.e., if someone manages to take out an enemy in a particularly vicious fashion, they'll become a barbarian, if they get killed without finding their class, they'll make a pact with an otherworldly patron to save themselves by becoming a Warlock, and so on).  

My question is, is there a way to set up character sheets for the players that don't have a class? I see that, as standard, the character sheet can't be accessed till a class is selected, but I wondered if there were a way around that, perhaps through some homebrew content. It's not the biggest deal in the world if I can't get it working - I'll just give them paper sheets till they get their classes, if that's the case. But I figured I'd ask. 

Make the sheets as a class with no real proficiencies or early stat-changing features like a Wild Mage Sorcerer. You can then simply switch the class later.

Alternatively, make NPC style sheets as homebrew monsters until they get their class. You can't add this as something they can edit on here but you can print them off.

Do note you will have to be considerate about Hit Dice. There is no real default for PCs and their Hit Dice are determined by their classes while monster hit dice are determined by their size category. It's not a big thing, but it is worth realising their HP can change significantly by switching from NPC sheets to PC sheets. For NPCs the basic hit dice for a Medium creature is a d8 but if they gain a class like Sorcerer or Wizard they will drop to a d6. You could start them as d6, but then they are effectively weaker than standard commoners. You could start them as d8 and keep that even if they gain classes that use d6 but then they are much hardier and this can be a balance issue compared to other classes (they have d6 hit dice to balance their significant defense spells and other magics). You could have everyone be d8 and stay that regardless of class but then you're making Fighters, Paladins and Barbarians - typically melee builds, into glass cannons and will go down a lot faster. While your idea is interesting this Hit Dice issue is going to be a nightmare to balance and keep fair. Then there's the immersion side of it if you're wanting to be a RP heavy route: the first class level represents years of practice, training, development and such as and a level 1 character is about 4 to 5 times as powerful as a commoner. It's a bit of a stretch to explain why they suddenly became so much more powerful. You can go the amnesia route but that would require them already having classes and discovering the class abilities in the game when appropriate (such as learning you have proficiency with Dex saves when encountering a physical trap or that you have magic when you tell them the spell pops into their head and they cast it).

I would also have a word about this with the players if you haven't already: not everyone likes being "given" a character and preferring to make choices themselves so you may need to really discuss your idea wth them and the impact it has. They can't very well come up with a backstory if learning all about magic as a Sage background if it turns out you've handed them the Fighter class.

Interesting idea but the implementation of it is going to be a nightmare given the problems it presents with backstory, background, what proficiencies are (years of training), what classes represent (years of training, super power boost compared to commoners), hit dice, and more.

Awesome, thanks for the suggestion. I'll probably go with the NPC idea. 

The story is that they're essentially playing themselves. I.e., they've been transferred from our world to the Forgotten Realms and need to find their way back home. One of my players said he wanted to do a campaign based on the idea of a bunch of people getting lost in the London Underground, and finding their way into FR, Narnia-style. Everything else has developed out from that idea. So their backgrounds will be based on their actual lives, and they won't need to come up with backstories and such - I'm going to give them proficiencies based on their real life stills. One is an actor, so he'll have proficiency in Performance & Acrobatics, another is a doctor, so he'll have proficiency in Medicine, and so on.   

As for the sudden stat changes when they get their classes - I wasn't planning on being subtle about it. It'll literally be 'You did thing X, now you've been magically imbued with the powers of such and such a class'. It'll require some severe suspension of disbelief for classes like fighter and barbarian, but hey, this IS D&D, and we're all pretty lighthearted gamers. The only player I can think of that might have an issue with it is the one that suggested the idea in the first place, so he's pretty happy to go along with whatever in order to get the story. I hadn't actually thought of the hit dice issue, but I think I'll just say they switch to whatever their class is supposed to have upon gaining their class. I can't imagine anyone complaining. Plus I intend to give them all an opportunity to completely reroll their characters, stats-wise, at the half way point in the story. I'm basically making the first half a survival game, and the second half a more typical heroes quest.   

Three of the five players are completely new to D&D, and I'm a first time DM (we're just finishing Lost Mines of Phandelver, then going onto this), so I thought this would be a fun way for us to all learn about D&D/The Forgotten Realms.

There are some books and movies that have a similar theme. Sounds like fun =)