This is consistent with my expeirence, though my highs are merely high 90s.
There IS a measurable (positive) heat difference a few inches from the panel on the underside, but its literally just a couple inches and only a couple degrees. Everything further from the roof panel is either ambient...
3/12 is the minimum effective pitch for metal roofing, 5/12 is better. If you have a 12' peak and 8' walls, you have plenty of pitch. A little overhang will help with our windowing rains some, and protect your walls.
I'm fond of metal roofing. Inexpensive and easy for amateurs to instal correctly - which is no small thing. Sucks to spend a ton of money and a ton of time installing and have it leak. Reflects a lot of heat, too. My coop is ambient air temp just six or eight inches from the metal, and shade...