Garage roof deck

I have a deck frame that I built on top of my garage roof where an existing deck was before. The city is giving me grief about things and said I need a structural engineer to approve my design and have it stamped (Iowa) before I can proceed. The garage rafters ad 2x12s spaced at 16" apart. I am not the most perfect carpenter but I spaced the joists 16in mostly and it is a 14x12 frame. The weight is dispersed over many different points on Tuff Blocks. I did not want to have to perfectly align the joists with my deck to the garage roof rafters so thus I made many points to disperse the weight instead of just 4 or 8 etc. The frame is about 3" off the existing roof and I built it with 2x4s. I notched them at 2" in and then glued them together with waterproof wood glue. I then put metal L clamps on each of the 4 corners where they meet. The city does not like my idea despite it being very strong. I explained it is just a frame to keep me off my shingles and the actual garage is the weight bearing structure which is in good shape and held a 2x4 deck before. This did no good. I am only 3" off my roof so argument sake say it failed (it will not) I would go about 3in to the garage roof which would stop the fall etc. All I need is something resembling my plan close enough with an Iowa stamp from a structural engineer to continue my build. I have talked to a few and one guy sounded promising but then shot me 5 inflated prices and when I asked specifically how much I would need to pay him got no straight answer. This tells me that he possibly talked to someone down town who is trying to thwart my build. I need to finish my project and would appreciate any help. I am open to modifying my design slightly here or there.