Hmm...well, the only reason to roll or do a point buy for stats is to see how you your character is at a given thing. I suppose you could define that by role, instead of by stats, by giving each role a certain set of skills and/or powers and/or some sort of "edge" over the others. Say, each role has four "basic" characteristics (same ones for each role, but different levels for each role), and a choice of three "Secondary" characteristics (so players still have the opportunity to individualize their character.)
So, for example, say the "Basic Characteristics" for each role are:
- Attack
- Defence
- Charisma (Social)
- Intelligence (Skill)
Each role then has a certain level in each characteristic; the Veteran might have a 5 for Charisma (because they've learned how to lead others) and a 2 in Intelligence (because their training has included more warfare than lore). These characteristics would be "ranked" at 2-5, with 5 being the highest; meaning that each role would have a 2 in their lowest stat, so they're not excluded from anything, just maybe not as good.
Likewise, the Rookie might have only a 1 in Charisma, but a 5 in Defense (because you have to learn to block a blow before you learn to land one). Or something like that. The trick here would be giving each role strengths
and weaknesses, so all your players don't just want to be the strongest role.
Then, there are a bunch of "Secondary Characteristics" they can choose from, which could be anything--maybe even things suggested by the player (with DM's right to veto, of course). These could be:
- Magic Knowledge
- Special Weapon Prowess
- Tactical Knowledge
- Morale Booster
- Healing Lore
...and so on. Each of these characteristics gives the player something different about their character, an edge over others; this way, the character's differences don't rely just on roles, and each of them can fill a niche in the party. Whereas the Basic Characteristics would determine how good a certain character is at one thing or another, the Secondary Characteristics would give them extra flavour and abilities.
So let's say I want to build a Veteran Fighter. My stats might look something like this:
- Attack: 4
- Defense: 3
- Charisma: 5
- Intelligence: 2
- Magic User
- Tactical Knowledge
- Special Weapons Prowess
So my character would be good at attacking things, but not great at defense; great at inspiring others to follow (or maybe leading an attack), but not so good at identifying magic items or monster knowledge checks.
Also, I've learned to use magic, and gain access to a selection of spells; I can use my Tactical Knowledge during a battle to give people an edge during the fight (think the Controller Role in 4e); and my Special Weapons Prowess means I'm able to fight with a
kusarigama, a weapon that has a basic attack, but also has reach and can trip or restrain enemies.
Or something like that. This gives you the ability to have players choose a role, but at the same time diversify that role to fit what they want to play (i.e."tanker/healer/caster or attacker/scout/defender or melee/range/spells etc" as you say below), while still having those choices have a mechanical effect on the game.
Then there's the question of how race affects it all. Maybe each race has a fourth Secondary Characteristic they get for free--Dwarves get Special Weapon Prowess: Greataxe, for example, or elves get Magic User. Then they get a racial modifier to one or two of the Basic Characteristics; Elves get a +1 to Charisma, or Drawves get a +1 to Defense.
Finally, there's the question of how the Basic Characteristics affect play. What does a 5 in Charisma mean? Does this give a bonus to a roll in game? Allow them to take certain actions that other players don't have access to?
Or maybe Basic Characteristics work the same as Secondary, and a player gets to select a total of three from a list of eight or ten, with the fourth being given for free by the Role.; I might choose Attack, Defense, and Stealth, for example, and because I'm a Veteran I get charisma for free. Each of those gives me access to certain actions/skills that I wouldn't have otherwise. That way there's no numbers at all.
Or is that moving away from what you're intending?