I'm making an infection map where the humans start in an L-shaped room, and after a while a dumpster moves out of the way to allow them out and the zombies in (like Manifest). Then I'm going to have the humans proceed through 'levels' if you will, where they have to hold their position and survive the zombie onslaught, while waiting for another room to open. Each room will be harder (less ammo, more places for zombies to get in from etc.), but at the end, the humans will have the advantage (might give them a Warthog turret or something). I'll throw in some other stuff, just to make the map more original and more fun. I spent an hour forging the dumpster opening mechanism and first room, so I'm hoping that people will be interested in my map idea.
Not really original, sorry. This is kind of a classic zombies game that is still fun to play, so go right ahead and make it. Nobody's stopping you.