The Ontario Fire Marshal (Canada) defines "Booth" and "Room" slightly differently:

Spray Booth means a power-ventilated structure that encloses or accommodates a spraying operation so that spray vapour and residue can be controlled and exhausted.

Spray room means a spraying area on a floor area or part thereof in which an open spraying operation is confined and that is separated from the remainder of the building in which it is located by a noncombustible vapour-tight separation.

In the absence of the OSHA letter I tend to think of a "spray room" as a totally enclosed room in which open spraying might or might not be conducted, but in which other spray booths might also be located. For instance, there are many coating shops in which an enclosed room houses several open-backed dry filter or water spray booths. Even though each booth is equipped with its own exhaust system, the room must be monitored for dangerous quantities of volatiles and perhaps it too will need an exhaust system. - http://www.paintcenter.org/rj/may05p.cfm