Zombie Outbreak

This is a post apocalyptic apartment crawl. Buildings are packed together. Survival is not guaranteed.

Proof of concept

Rules
There are always 1d4 zombies when encountered

DM Moves
Elevator Shaft - the DM can place one elevator in any building over 6 floors. The operational status of which should be entertaining.
Fire - once per campaign the DM can have a building catch on fire as long as the party is inside of it and it's hard to get out.

Depth Rules
At  1 Depth, a -1 Depth = an exit to outside
At Max Depth, a +1 Depth = the rooftop

Max Depth = Building's total floors

Add 1 zombie per Depth level when encountering zombies
Go up one letter on the loot table per Depth Level

3 Random Plot Hooks