This type of metal roofing has no exposed fasteners. The panels snap or lock together and are often held in by cleats that are fastened to the roof deck at the panel seam or by a tab near the edge of the seam that is covered by the next neighboring panel. This is usually done in steel but sometimes is done in copper. 29 gauge steel is the thinnest and least expensive option. We prefer 26 gauge at minimum but ideally the thicker 24 gauge steel. With thicker steel there is less oil canning(rippling during temperature changes) and it holds up better to wear and tear as well as hail damage. It also provides a better fit and finish overall. Do keep in mind, all steel roofing is subject to oil canning, this is unavoidable and will come and go with temperature changes.