My antenna is about 20 or so feet up, and I have a FM antenna below that antenna, and I have the main line going into the top part of the attic, where I have my 4 way splitter at. It gets extremely hot up there in the hot months of the summer. I sweat like I'm in a shower if I half to go up there to fix something.
The higher the amp is, the farther away from the roof it'll be and the cooler it'll be in the summer; but even if it's mounted at a convenient height of 4 or 5 feet above the roof it'll still be cooler than in a typical attic. Mine's on the antenna mast about 4 feet above the roof and it's been chugging along for 3 years without problems.
Still, if I have to get on the roof during a summer day, first I turn a water sprinkler on the roof for about 5 minutes, then let it dry for another 5 minutes or so. A little evaporative cooling works wonders.