So we can make this any theme, original or existing? Sounds neat, can't wait to see what people come up with.
I think I'll enter this as well. Even if I don't win, I know I'll get quite a bit out of this, and I find giving life to maps is always fun. Layouts have always been the thing to halt me in making maps, but now that I have a layout done, I can see how well I can truly do in the detailing department.
Good luck to everyone else entering!
Edit: The way I see this, I'm less concerned about how it plays, and see this more as a "Give life to this map, let us worry about the gameplay" type of deal. I'm positive Valve will fix what they have to concerning balance, which is why they told us not to alter anything that affects the gameplay.