There is a car park near here which is partly [ground level open parking][1], and [partly multi-storey][2] - I added `building=carpark` in this example, though it has the same effect as `building=yes` in most use cases that I am aware of.
I probably added the building tag manually afterwards.
afterwards (and yes, building levels would probably also have been a good one to add)
[1]: http://www.openstreetmap.org/way/72855139
[2]: http://www.openstreetmap.org/way/72855168