I posted on here last year with a pic of a guy re-roofing his home using galvalume over his existing asphalt shingles. He was doing it himself. Now across the street and caddy corner to my place, there's a crew doing the same thing on a neighbor's house. I went over and chatted briefly with the foreman. He works for a local roofer who got the referral from the company that supplies the galvalume....whom I have also purchased from.
I am planning on doing my roof the same way this fall/winter. My roof is very simple, unlike my neighbors!
I like the plain galvalume look but you can also get colors. But the regular galvalume would reflect heat the best. You can also get different styles of sheeting...like standing seam. The ones used in the photos are just called ribbed.