i think it depends on how close the building is to your camera and how much focus it gets in your scene. if it's in the background - i would just texture the windows.
if you want more detail, i would model one floor and it's windows, duplicate it, put the duplicate on top of the first, combine and merge them - you will now have two floors. duplicate this and put it on top of the original and you will have 4 floors. do it again and you will have 8 and so on - once you have the first floor it will take two seconds to build the rest of the building.
by the way, is that echo red?