I am making a spellcaster barbarian and am having trouble deciding between wisdom (druid flavored) or use strength/charisma(intimidating the weave of magic)

As someone who activated rage can't do spells/magic/etc.  A spellcasting Barbarian is tricky to play.  Combat spells will not be very helpful, buff spells would be useful as long as concertation is not involved.

I would say it should be intelligence so they can better understand when to rage and when not to.

i am making a homebrew subclass that can only do evocation spells and only while raging

I wonder if constitution could make sense? Flavoring it as them using their raw physical endurance to force magic to happen? Idk I just like to see weird applications for CON

Quote from BaconBreadman >>

I wonder if constitution could make sense? Flavoring it as them using their raw physical endurance to force magic to happen? Idk I just like to see weird applications for CON

 That is a great idea

Quote from Character77006 >>

As someone who activated rage can't do spells/magic/etc.  A spellcasting Barbarian is tricky to play.  Combat spells will not be very helpful, buff spells would be useful as long as concertation is not involved.

I would say it should be intelligence so they can better understand when to rage and when not to.

 There's nothing tricky about spell casting as a Barbarian. You aren't Raging from the time you wake up to the time you take a long rest. 

The spellcasting attribute would depend on what spell casting class you use: Druid= W, Wizard =I etc. 

While there are Barbarians who use spells - such as Wild Heart - these are almost exclusively out-of-combat utility. Rage is the central mechanic of the class and the class is crippled without it. Indeed, due to Primal Knowledge you'll often see Barbarians Raging out of combat.

So I'd question the premise. A "Barbarian who casts spells" sounds a lot more like a Druid than a Barbarian to me.

Quote from VerilyRaze >>

 Rage is the central mechanic of the class and the class is crippled without it. Indeed, due to Primal Knowledge you'll often see Barbarians Raging out of combat.

 

That's your opinion. Barbarians don't rage 24/7. Players can decide for themselves when they want to cast spells or when they want to rage. I don't know if it is the Youtubers coming up with this and people just get on board because they saw it in a video, but there is absolutely nothing wrong with wanting to dip into a spell caster class or take the Magic Initiate Feat route. 

Charisma as it would be a force of personality that thematically pairs better with rage than trying to be Wise while raging.

Also, I would not have it be casting spells but instead Invocations/Chants/Shouts. Nothing that requires concentration.

Quote from HawkwinTenebrae >>

Charisma as it would be a force of personality that thematically pairs better with rage than trying to be Wise while raging.

Also, I would not have it be casting spells but instead Invocations/Chants/Shouts. Nothing that requires concentration.

 Rage doesn't just limit you from using concentration spells: you can't cast any spells at all. 

Quote from FlameOutsideOfStaff >>

i am making a homebrew subclass that can only do evocation spells and only while raging

 Having Evocation be the school of spells that you cast feels a little like putting a hat on a hat. You have a character who excels at doing damage casting damaging spells. Also, one of the (IMO deliberate) limitations of the Barbarian is that they're one-on-one fighters. These limitations exist for a reason - if you can kill enemies solo and manage crowd control, why have a party caster? Hell, it sounds like this character could kill an enemy solo while managing crowd control.

Instead of school-specific, I'd suggest making a short spell list of thematically appropriate spells (things like Cause Fear or Enlarge/Reduce are Barbarian staples, while spells like Compelled Duel or one of the smite variants might augment the solo-killer element rather than confound it) that the Barbarian gets at certain levels. It might help control the scope of the class and inspire future class features.

Either way, Con is the saving throw that previous spellcasting-adjacent Barbarian subclasses have used (see Wild Magic Barbarian from the 2014 rules), so I'd start there. That said, as Con is an essential Barbarian ability score that also provides bonuses to Concentration, hit points, and one of their saving throws (which, consequentially, also provides Concentration bonuses) it is even more critical that you not make the spell list too OP.

The Spell Scorned Barbarian subclass in Cthulhu by Gaslight explores this design. The mechanic they use for casting spells while raging is:

"When you activate your Rage or as a Bonus Action while your Rage is active, you can cast [spell name] without a spell slot or components while your Rage is active, and your spellcasting ability for it is Strength."

Quote from MPA >>

Quote from HawkwinTenebrae >>

Charisma as it would be a force of personality that thematically pairs better with rage than trying to be Wise while raging.

Also, I would not have it be casting spells but instead Invocations/Chants/Shouts. Nothing that requires concentration.

 Rage doesn't just limit you from using concentration spells: you can't cast any spells at all. 

Go back and read the second sentence.

I'm a bit late to this one but I'll throw this at the wall and see if it sticks:

Have Cons for spell-casting ability but instead of giving them spell slots they have to burn Hit Dice to cast spells, each Hit Dice equals one spell level so to cast a level 1 spell they burn one Hit Dice, a level two spell costs them two Hit Dice etc. Then give them a spell progression equal to an Eldritch Knight or Arcane Trickster that way at 20th level they would know a max of 13 spells none of which would be higher than 4th level.

Quote from Rob76 >>

I'm a bit late to this one but I'll throw this at the wall and see if it sticks:

Have Cons for spell-casting ability but instead of giving them spell slots they have to burn Hit Dice to cast spells, each Hit Dice equals one spell level so to cast a level 1 spell they burn one Hit Dice, a level two spell costs them two Hit Dice etc. Then give them a spell progression equal to an Eldritch Knight or Arcane Trickster that way at 20th level they would know a max of 13 spells none of which would be higher than 4th level.

 That's really smart!

I say: Constitution or Charisma. Both of these suggest that the magic the Barbarian is using is innate.

Maybe it's a manifestation of their fury. A barbarian shaping their own rage and anger into spells takes a lot of willpower and confidence, so Charisma is most fitting.

But if it's a barbarian who is magical but cannot control their magic, it should be Constitution. Wild Magic Barbarian's powers are based on Constitution. And "a barbarian who is magical but cannot control their magic" is basically the definition of Wild Magic barbarian.

I say Wisdom, since the only current spellcasting option for the Barbarian, -a subclass- seems like it would fit with Wisdom, and Druid spells fit the Barbarian most thematically.

Charisma would be my second, as both Barbarian and Sorcerer have a 'Wild Magic' subclass so there's already a connection there.

Constitution as a spellcasting ability would be kinda OP, I feel.