Not in the building, but in the parking lot a few times. We fooled around behind a little shed thing a lot, and we fucked in a friend's truck parked in the lot once. It was fun.
My ex and I had sex in the place his mom worked once, though. It was a physical therapy like place, located in what was once a house, and we had sex on the closed off stairwell that led up tithe boss's office and living quarters. He was in there at the time, and his mom was working. We went to bring her something or get something from her, and on our way out we slipped into the stairwell and had sex. Lots of fun, apart from the physical difficulties of having mostly clothed sex on stairs.