Given the idea is zombie themed... you could have a set number of people and one zombie. During the day everyone votes to eliminate who they think the zombie is. During the night the zombie can infect a player, turning them into a zombie. The zombies win if they take over a set majority of players, like say 2/3rds or so, and town wins if they kill off all the zombies. Since the concept favors the zombies a bit you could have power roles that don't transfer over if someone gets zombified, and have just the first zombie able to bite and recruit someone.
Now I'm a complete novice at mafia planning, but since the film (I don't really count the others as they kinda suck) had a zombie infectee the concept might work. But this probably needs a lot of refinement. ><