I figured I needed a place to put this for ease of mods that do nonstandard teams or wanted a good phrasing for their win conditions.
I made up a list of about 12 alignments that I think should cover most of your bases. If you feel there should be more explanation, please say so, and I'll update it.
Town - You win if there is someone alive from your team and all scum factions have been eliminated (Mafia, SK, Cult).
Mafia - You win if there are no other killers alive and your team equals or outnumbers the number of remaining players. You may make a mafiakill in lieu of your normal abilities.
Survivor - You win if you are alive and another faction wins or if you are the last player alive.
SK - You win when all other players are dead. (This may or may not require being alive.)
Cult - You win if there are no killers alive and your teams equals or outnumbers the remaining players.
Jester - You win if you are lynched. (This may or may not end the game.)
Lyncher - You win if [PLAYER] is lynched and you are alive. (This may or may not end the game. Typically if your target is killed, you will turn Town.)
Martyr - You win if you are killed. (This may or may not end the game.)
Assassin - You win if [PLAYER] is killed and you are alive. (This may or may not end the game. Typically, if your target is lynched, you will turn Town.)
Ally - You win if [ALIGNMENT] wins. (This is typically called [ALIGNMENT]-ally, e.g. Mafia-ally, SK-Ally. This does not require you to be alive, but you do not count in alignment numbers; e.g. if there are no more Cult members alive, you can no longer win, as you do not count as Cult.)
Brother - You win if [PLAYER] wins. (This does not require you to be alive.)
Watcher - You win if Day [DAY #] is reached through normal gameplay. (This may or may not end the game, which may overlap with a Doomspeaker. This may or may not require you to be alive.)
Outsider - You win if [NONSTANDARD WIN CON]. (Outsiders may have any wincon, or even no wincon. This may or may not end the game.)
EDIT: And while I'm on the issue of nonstandard gametypes (like BYORs), I have a nice template for roles, as well.
You are Example (Alignment).
Role Name - Player Name
Abilities:
(Auto) Example: This is an Auto ability that happens in response to something.
(Mafiakill) Example [target]: This is an ability that replaces the normal mafiakill ability. You may only use it if no one else is using the Mafiakill.
(Night) Example [target1] [target2]: This is a Night ability that actions target1 and target2, though not necessarily the same action.
(Day) Example [target]: This is a Day ability that actions the target. It is used during the Day.
(1-Use) Example: This ability can be used anytime. It can only be used once, and after that it is used up.
(X-Use) Example: This ability can be used anytime. It can be used any number of times. This is a rarely used type of ability.
These ability types may be mixed and matched to create abilities.
DOUBLE EDIT:
If you plan on creating a BYOR, try to start small first. Yes, lots of roles and actions make a fun game, but not being able to keep track of them is frustrating. Also, never overpower one team. It turns out not so well. For overpowering, see the Cult in BYOR 4, which gives a Reviving Hiding One-Shot Paranoid Gun Owner Cult Leader. I'd say if I removed the PGO, it might have been better, but once you learn how to make each side as powerful as the other side, it can get really crazy.
Examples:
Cops: Godfathers add an element to Cops to stop them from confirming people, while adding no other problems to the game. Adding a Frame Artist is even MORE effective, since it wastes a Mafia Night action to use, as opposed to an Auto ability, and doesn't always work.
Town Roleblockers: These roleblockers are much less helpful. Mafia roleblockers can always hit Town, but a Town RB can only sometimes hit Mafia, and rarely hits the Mafia killer.
Third Parties: Have at least 1, and try to keep the ratio about 10-20%. If there is no Mafia, this can be as high as 30-40%, but you should have a Mafia.
Serial Killers: If you add an SK in a BYOR, their being alive should not be required. BYORs get kill-happy, and a revive on an SK isn't a bad idea, though be careful not to overpower an SK.
Underpowered Teams: If you have a team that is seemingly disadvantaged in some way, add either a Brother or an Ally to their cause. However, that is only for minor boosts in power.
1-Shot Powers: A nice limiter on a player's role are 1-Use abilities. 1-Use abilities are highly regarded and tend to be used less often, mostly because they are rarer.
Cults: Cults are very powerful. Find ways to limit a Cult's effectiveness, if necessary. The bigger a game is, the more limiting a Cult needs.
Revives: Don't use them if they revive after role flip, or if you do, use them veeeeery carefully. See BYOR 5.5 for how NOT to use them.
Balancers: This is very important. If a player has a potential of breaking the game, make sure other players have these. A Balancer is an ability that counters a Game Breaker. It might be something small, or it might be something incredibly big. The key is to make sure there is at least 1 way to counter any strategy. I tend to have 2-3, especially after my mistake with BYOR 5.
Doctors: You should have at least 1 Doctor ability, if not a Doctor role. They're small but helpful.