Great project you have going. Your question for tips on screwing the corrugated roofing panels on an existing patio cover is something you definitely can do yourself. First you need to pre-drill the holes on the corrugated roofing panels. Start by placing one panel at a time on the rafters and cross brace. Place the closure strip on top of the corrugated metal and drill through the closure hole in the valley. This uses your closure strip like a template and ensures the panels and closure strips are aligned. You can screw/nail the closure strip to the cross braces using exterior rated fasteners.