It's all contractual. A star will get their choice (or will get promised the biggest one or best-location dressing room) and may also get a stipend to decorate it.
Most Broadway theaters move vertically so yes they span multiple floors.
For a large-cast show in a house with limited dressing rooms, it's all a matter of numbers so some principals may be 2-4 actors to a room. Bette had two dressing rooms for DOLLY (one for receiving guests & lounging between shows, and one that she used as her actual dressing room during the show).
The actual assigning is done by the company manager in consultation with stage management, GMs, producer, etc. to try to make the space work best for the most people.
"Dressing Rooms" also have to be used for a stage manager office, usually the conductor gets a dressing room with a piano (where impromptu vocal rehearsals or warmups can also occur), there may be a musician dressing room/green room, sometimes band members are playing out of a soundproof dressing room and not in the pit (such as DEH)...etc.
Jackie Hoffman's ADDAMS FAMILY video series showed off Broadway's nicest dressing room, the star dressing room at the Lunt, which is huge and has (among other things) a full bathtub installed for Liz Taylor. The Beaumont's dressing rooms are also quite luxurious.
Updated On: 4/11/24 at 11:53 AM