There is a multi story building in my city that is all rented out to various bands for rehearsal spaces, photographers for studios, there is a dance hall, a recording studio, etc. How should I classify this feature?
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Welcome! amenity=studio (OSM Wiki) sounds like the closest fit to me!
I’m usually able to find these more obscure tags between searching the OSM Wiki, OSM TagInfo, and OSM TagFinder! 
If it’s just a commercial building with leased space, not much can be done in terms of its description – it’s just a building=commercial.
Individual (long-term) renters can be tagged using multiple points within the building outline, with tags as appropriate: amenity=studio, amenity=dance_school, craft=photographer, club=*, …