Hi, Well I am still dumbfounded as to why folks are responding to this question about metal roof and steering novices to installation of metal roof in the wrong direction. Please do your homework. The only time you install a screw in the corrugations of metal roofing is at the lap of one sheet to another. Called a stitch using self tapping sheet metal screws with rubber or neopreme washer.. Otherwise, metal roofing manufacturers and installers call for the screws to be in the FLAT area of the panel an inch or so away from the corrugation. This is for holding power and strength of the roofing system. If you install the screws designed to hold the roof down in the top of the corrugations, you run the risk of overtightening the fastener and deflecting the metal, causing a potential leak. I have installed hundres of squares of metal roofing over 38 years of construction/ remodeling work and have never had a leak problem installing it the proper way with the appropriate fastener and technique. Next time you are close to a metal building that has been erected by a professional, take a closer look and see where the screws are positioned.
Erik