So I can guarantee to you that I will be making a city themed map at some point. I wanted the map to focus on some of the more urban areas of a city while remaining in industrial areas, almost in a transition district from dirty industry and warehouses to some sort of lower-class neighborhood. (It just doesn't make sense in a high-wealth commercial/residential area).
One of my first ideas was for some sort of secret base located inside a bank. This was the first building I made, and although it might look very pretty, there are hundreds of brushes; so its not the best idea for gameplay.
I might, however, try to simplify the geometry so that there is only 1-2 layers of detail instead of around 6 which it currently has. (At this current rate of detailing I would surely hit a limit, probably melt my computer in the process.)