Yeah, that's wrong. The inspector ought to know better; clearly does not inspect a whole lot of commercial installations.
Gently stand up on the point and show him the code, and leave him a path to keep his ego intact (that is less than you pulling a bunch of pointless ground wires). That's part of negotiating.
By the way, if you do pull the trigger on ...
Basically not without chiseling (or drilling and chiseling) in to find rebar (and it would have to be a 20 foot chunk unless it was all tied properly for use as a ground even though you forgot that part at the time.) Covered by 2" concrete is not actually inaccessible, particularly if the concrete is relatively fresh/green. You can do that, and patch ...
Yes it will be a problem. Not sure where you are but in my home country and minimum of 8 degree pitch (approx 1:7) is required for long run sheets, and 10 degree for end lapped sheets by the building code.
If you don't you may have the following problems:
Pooled water that will shorten the life and void warranty on the corrugated iron
Potential leakage ...
Some great suggestions and I did get a shorter 5' piece of the 2 1/2" IMC threaded and did exactly what Freeman and Ecnerwal suggested. But to answer my original question:
Answer: The final top section of IMC conduit needs to be securely tied to the structure by at least one strap/tie. (This is from my interpretation of my local codes and discussions ...
Why not simply flip the riser upside down, so the 3' section goes directly into the meter/main, and the 10' piece goes up through the roof into the weather head. That way you can easily get two clamps between the coupler and the roof line, securely holding the 10' piece, and 1 clamp on the 3' piece between the coupling and the panel.
I agree; you have exposed a very serious flaw.
Go look at Google images of quonset huts. All of them either have
a) vertical ribs on the sides, or
b) horizontal ribs, but a vertical-rib "cap" about 10 feet wide at the apex of the structure. This is bent in the "tough to bend" direction.