Would be a very unique and cool map idea to have the entire thing set in a multi-floor section of a skyscraper where you can fall off the side, break down the floor/walls to go between floors, and have a ton of verticality.
For an example of what the map can look like, please google "new york city" or something. It would only be like the top sections of a skyscraper. Helis could be the only vehicles, but that might be pretty sick as well.