If you want the best there is, consider ASCBP'S 26 gauge Standing Seam Skyline Metal Roofing.
"ASC Building Products has enhanced the performance of Skyline Roofing® with the DuraTech® xl coating system. Available in a wide variety of Cool Colors formulated to reduce the demand for energy. This coating technology integrated with Zincalume® coated steel provides a lifetime of durability."