The only thing that I could add to your fine explanation is that your comment of the slope being 9\11.
If you were using the square to layout the cuts bottom and top of the rafter you would use 9.81 (plus a little bit more) inches in 12 to arrive at the 108 inches rise in 11 feet of run.
Thanks again for the quick response.
You would wonder how or why they asked for this particular roof slope, rather than one that would have been an even number say 10 inches rise in 1 foot of run, it would have only raised the peak approx 2 additional inches.
