To find sections that do not have a room assignment, you can use the filter option and in the Course section input your department or subject code a search AND in the Room section for "University Classroom.  You can also see sections without a room in Banner at the Provost’s Website (instructions to view this are in the handbook).
Fall 2017: https://workingcatalog.gmu.edu/wen/201770/search/#mrn=University%20Classroom
Spring 2018: https://workingcatalog.gmu.edu/wen/201810/search/#mrn=University%20Classroom
Helpful Hint: If you want to use a university classroom that is on a section you are deleting, for another section, submit your deletes first to clear the room.  Then type the room in the Internal Notes box on the new or modified section that you want placed in that room and submit again.  Be sure the new section meets on the same days/time as the deleted section.