From
http://suite101.com/article/shingle-roofs-vs-metal-roofs-a32169
"
The lifetime of the composition shingle is 15 to 30 years . . .susceptible to algae growth. . .an anti-algae coating are more expensive. . .Cooling can be further enhanced with radiant barrier paint on the underside of the roof sheathing.
. . .can expect to pay about 30 percent more for a metal roof. . .steel roofs are a good choice for areas that experience high winds. . .metal roofing material only weighs approximately one seventh what a shingle roof does, putting less stress on the house's structure. . . Steel roofs are fire proof which is not only safer but may result in a lower insurance premium. . .Most metal roof manufacturers will give a guarantee of around fifty years but experts believe this is a conservative estimate. . .Some look like conventional shingles and others look like cedar shake shingles.
"
So comp shingles do better in cooler temps.
$4,000 = comp shingle cost
...............cost/year
15 =life in years $267
30 =life in years $133
$5200 = metal cost, comp cost + 30%
...................max cost/year
50 = min life in years $104
BUT, half the people move in seven years and almost all have moved by 14 years.
Decisions, decisions. . .