Web's guide to making a role:
Alright, first and foremost, a role must contain the elements of CHOICE. Players LOVE choice. It doesn't matter a whole lot what the choices are, but you want the ability to choose something. Like, having two actions. Or one that lets you choose a player. Like "(Night) Choose [target]: Choose One - Inspect the target; or Track the target."
Second, be a little flavorful. That's not that big of an idea.
Third... Make it feel powerful. Now, not everyone needs a kill, but if you can make a role feel like it has an impact on the game, it's even better than one that doesn't feel useful, but actually is. A simple ability like... "(Day) Sacrificial Lamb: Remove all abilities in your role. Gain a copy of any action that targets you during the next Phase." It's a choice that can be insanely powerful. But, it might not be.
Fourth, synergy between abilities. If one of your abilities is an Inspect and the other is a Kill, there is some synergy there. If one is a Hide ability, and the other is a Protect, the synergy is still there, since you have the choice to protect yourself or protect someone else.
After these four, you're really looking more at advanced topics. Things like making roles unexpected. Sometimes, a Town player should have SK abilities. Sometimes, a Mafia player can be played as a Town Confirmer.
Oh, and last note: Never have a Cult. They're hard to balance.