You can use zones to light an entire zoned area, or your entire building granted if it was one zone, but that would look fugly
You can also do what DeRailer said, that would definitely work, but why would you want to use one light to illuminate a entire building? That wouldn’t look very real, but then again I haven’t seen the lay out so I can’t say for sure.
Lighting is a pain in the a$$, but is one of the most important things to take into consideration, it is the mood and the dynamics of your map.