I went on the Sofi Tour last week.
The canopy is not attached and basically "blankets" the entire stadium, and it's MASSIVE. It's basically a HUGE PATIO that allows for shade and comfort. Air flow is easily attained because the "roof" towers over the stadium.
The roof can open up sections (like cracking open your sunroof of your car) to release hot air and computers can regulate the stadium temperature.
In fact, the entire stadium is made for all you "Tech" guys and the amount of wiring used in the stadium to keep the computers talking and getting world wide internet can wrap around the entire world.
FWIW, employees think it's going to be a HUGE HOME FIELD advantage because they say it gets loud and they crank up the volume on the OCULUS, so the place will be rockin' on game day.