HOLD ON, i first wrote rules for this very same idea back in 2013.
Last Days: Zombie Apocalypse is a skirmish-scale miniatures game of survival horror. It pits players against each other in a nightmarish near-future where the dead have returned to life and are feasting on the living.
Players build their own factions, representing desperate civilians, military personnel, or hardened survivors, and must explore, scavenge, and fight in order to survive another day. Rival gangs are only one of the dangers they face - mindless zombies wander the streets, driven by insatiable hunger and drawn by the sound of combat!
A gang's ability to scavenge is as vital as their combat ability, and players must ensure that they have the resources to survive in this hostile world. Scenarios and campaigns allow you to develop your gang, gain experience and recruit new henchmen to build up your strength or replace the inevitable casualties of the zombie apocalypse.