Once I get the garage built, I'm going to re-roof the entire house so all of the old and new match.  The existing roof is shot anyway; but I'm limping it along as best I can... one tube of roof sealant at a time.  Currently have standard asphalt dimensional shingles (Owens Corning); but I am 90% decided on a standing seam metal roof with hidden fasteners.  The research I've done says the clip fastener style is "better" than the ones with pre-punched fastener holes because they better allow for movement as the metal expands and contracts with temperature variations.  Aesthetically, the product needs to be available in a charcoal gray color to go along with the existing color pallet of the rest of the house.  Current shingles are the "Estate Gray" color offered by OC and looks really nice.  I've ruled out the metal shingles because part of the house is a 2.5/12 pitch and all I've found are only warrantied for > 3/12.  So what specs would you say are crucial for a metal roof in central Indiana?

Material? (aluminum vs "galvalume" or other steel offerings)
Minimumm thickness?  Seeing mostly 24, 26, and 29 gauge?
Coatings / paints?
Felt underlining for condensation control?

Here is what I am currently considering:

http://www.fabral.com/post-frame/panel-systems/standing-seam-panels/1-and-a-half-inch-ssr-post-frame-metal-roof-and-wall-panel-system/