I created the mechanics myself, but you can tweak on it if you wish to make the game as balanced as possible
Can probably tweak the roles so that it doesn't have to have buildings, suicide bomber for example would be able to take out two people but sacrifice him/herself and instead of a Defuser you'd have your standard doctor
If he has an idea for a theme and that's why he's offered to run a game it stands to reason that he wants to use his idea's...