How tall is this building?

Orbiting isn't zero gravity, it is a sort of perpetual falling. When falling, everything is in the same place until some energy is added and things drift apart. The building would have to be as high as the the geostationary point which is quite high. Orbiting isn't really centrifugal force, just a vector change due to gravity so the track never goes back to Earth.... There are actually very few places in the Universe with zero gravity, but you can get close. Actually just thinking about it and there may be a centrifugal force, but it may not be significant until pretty far out. Maybe beyond the geostationary point, because objects are in collapse until then, if moving with the Earth's rotation.