my choice would be a LPC9xx (<$1) per floor if it was a real building.
The problem here is that easily the electronics can end up taking up more space that the building MODEL.
If every lamp was to be controlled centrally, there would be 3000 wires (imagine the thickness of the bundle) coming out of the model.
One pertinent issue re saving volume of electronics would be: is this to be used in a low EMI area and can a single miss now and then be tolereated. In that case 3000/8 shift resisters with latch could be employed.

Mahmood, could you inform re the size of the model, if it is displayed indoor the floor to ceiling of each of the 50 floors can not be more than a few inches.

Erik