Flashing is a "L" shape thin layer of metal sheet used to cover the gap between vertical & horizontal wall. the best method is as forumer here.to cut the wall with grinding disc and tuck in the bended tip into the wall, nail on to the wall with what either method. then seal the side with silicone or equivalent...



G.I is a coating.. zinc coating. best is to use PPGI(pre-paint colour G.I sheet) better than G.I alone due to its service environment(subject to rain spalsh & sunlight)