So easy, find a room with only one door. Get the big barricade, one laying flat and one standing up. Stand on top of the baricade and repair it while killing zombies, live forever. :D
This has lots of potential. Make it multiplayer for one, chose your own character (or customisable characters) buy items and wepons ingame, while you still make barricades at begining. These are ideas for a multi version if you decided to make one.