
With a steel deck and structure, you are going to have a hard time fastening to the metal trusses with normal self tapping screws.
Do you have a typical fastening approach to a 9" roof section? Is it common to fasten the roof through the whole assembly.
For context: Steel deck, with rock wool flute inserts supported on cold formed metal trusses; R-38 insulation is above the deck, standing seam metal roof. The roof slope is 2.5:12.