Aluminum versus galvalume roof

Have you ever heard of nailing Gavalume corrugated roofing in the valleys instead of on top of the rib?

Are you talking cost, wind performance or resistance to salt and on coated or uncoated product product. Generally speaking Aluminum costs more then Galvalume. There are differant weights of metalic coating on Galvalume designated as AZ 50 or AZ 55. The AZ 55 provides better protection than AZ 50. Painted with a high quality PVDF, they will both provide good salt resistance however the Aluminum is better in direct salt spray environments. Galvalume based products generaly have a superior wind resistance rating. I would select a product and check their approvals and make sure that they meet the building code requirements as this may be the governing factor. Then look at cost and do a life cycle analysis.