I encountered some buildings today (1 through 2) that appear from the front to be building:levels=2, roof:levels=1 & roof:shape=saltbox and from the back just look like building:levels=3 & roof:shape=flat. How to se feel about tagging things like this? At present I have tagged them according to the first set of tags as that’s what you’d see when trying to visit them, but I’m not sure if this is right.
I know we have a convention for which levels count as basement with sloping ground, but do we have anything that covers roofs that don’t know whether they want to exist depending on who they’re facing?
I think if the roof is complex like that, the good answer is to start using building:part tagging. If you really want an answer for an overall tag – the “main” or “most prominent” style of roof. I think that’s what StreetComplete recommends.
Saltbox variations documented also on the 4D roof shape wiki Search results | OpenStreetMap Taginfo
The basement part i did not catch, you’re saying building:levels:underground? We’ve got many here, a classic where the street side looks like 5 levels apartment block but when viewed from the other side of the valley its 7. On entry you take the elevator down if you live on the 1st floor. Ground is garages. Steep driveway on the north end. The wiki says a walk out basement would be level=0 Key:level - OpenStreetMap Wiki