I'd probably have some pins that go through the table and are secured under the table. Perhaps you could use something like a large washer and a cotter-pin to hold them in place. For lighting, a hole with a fixed connector mounted flush with the bottom that you'd just plug the lighting harness into.
With this setup, you could just reach under and pull the pins and connectors and then lift the buildings off. On our modular club layout, many of the buildings are on small landscaped foundations that all lift off with the building.
