Not more than a few days ago, Valve finally released their long awaited SDK for Left4Dead and I promptly set about making a survival map that I've had bouncing around in my head for a while. The concept was that, instead of a single area with a few defense points that is typical of the standard suvival maps you have have a larger area with multiple "checkpoints" that you could fall back to. The ideal set up for this kind of gameplay is a military bunker, set into the side of a cliff. You start outside, fall back to an inner chamber and can close blast doors that will hold the infected at bay for a time. You repeat this process two more times falling deeper back into the bunker until you reach a command room where you can run no further and make your final stand.
I used SketchUp to lay the map out:
I actually have all of this laid out in Hammer already, but I'm having some difficulty getting the director to cooperate with where I want zombies to spawn in from. It has to do with the navigation mesh editing, which is only done in Left4Dead. Well it's kind of done in Counter-Strike: Source, but not to the extend you need to do it in L4D so I'm still getting the hang of it. Once I do I'll have a beta version up for download. At the least, expect screenshots soon.