Technically you may be right, but with my coop open on all four sides and 8 foot height inside coop there is no accumulation of heat inside the coop unless I close up sides for winter when I want to keep some heat in and drafts out. Hot summers/cold winters here. Can go over 100* frequently in the summer with high humidity, and the coop is always at least 10* cooler than outside. Air movement and lots of deep shade from the deciduous trees is the key, and who cares if those trees drop their leaves on that metal roof! Lol Winter time sunlight can hit that metal roof and warm it up, but at that height it doesn't accumulate enough to increase the temp inside the coop even when its in negative degrees. Wish it did.
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 air temp or cooler (from the shade).- though I don't see 10 degree differences typically.
I took readings earlier this year. Will do it again now, we have an almost cloudless sky ATM, panels have been in full sun all day.
/Edit -
Outside temp, 82.6, winds 10-15, gusting higher.
Coop roof temp, 95.8 maybe .9, it was waffling a bit
Inside coop (4.5" from underside of metal - thickness of a 1x4 plus a 2x4 long) 84.5, call that 2 degrees.
Inside coop at chicken level (greater than 36" below roof), 82.7
Temp at ground/floor, 82.0