The flat black asphalt roof over my apartment gets very hot, so one sunny day in April, I painted it white. (Click on the photos for larger versions.)

My roof before I start: black asphalt, flat, and very hot.	I used an 18"-roller, tray, and a 5-gallon bucket of oil-based white primer.
3 pm, and about halfway done.	4 pm, and almost three-quarters-done.
You can see how much sun (and heat) the white paint reflects away from the roof.	I got a 3/4" "rough" nap so the paint would fill all the irregularities in the asphalt.
My friends J and R, pictured here...	...took this picture of me standing on the finished roof. Then we had beers.
Looking out across the rooftops to the west...	...and to the south.

Searching on the Internet suggested I'd need special expensive "elastomeric white roof paint," but the $89 5-gallon bucket of good-quality oil-based white primer went on evenly and should weather well. (Although the bucket said each gallon would ideally cover 400 square feet, one 5-gallon bucket was just enough to cover my 1200-square-foot roof using an 18-inch roller with a 3/8" nap.) Someday I'd like to even put solar panels on the roof, but for now, $160 and a Sunday afternoon don't seem like too much give up for the satisfaction of a much cooler third-floor apartment, and both Obama's climate guru and the Houston Chronicle's Science Guy agree whiter roofs might even help mitigate global warming.