I have been contracted to wire a small free standing office one story wood on slab construction approx 25 x 25.

It looks like a romex job, but I have been told that the inspector wants MC cable. His reasoning that it is a place of assembly.

Bldg has it's own service and will be used a an office to rent self storage units.

With my understanding of the code single story commercial, romex is acceptable. Place of assembly means 100 people or more, and bx would now be accepatble there also.