Okay so simply put there is a frame of giant house, that is indestructible(Is this possible?). All the players act as survivors, and they can build fortifications within the house. You can have zombies that are AI that enter everywhere. They can destroy blocks, climb stairs, and attack. Basically the players have to survive round after round.
Also if needed, there can be a re-build time between rounds.
So... what do you think?