I glue roofs on all the time but only full skins not sections that half roof would be a good candidate for a tig welder but it sounds like that is not in the cards wen you do weld it you need to stop the heat transfer so it doesn't buckle from the heat you can do that by putting clay on eather side of the seam a cheeper way is wet newspaper cut in strips or folded in strips the wet paper or clay will absorb the heat and stop it from traveling threw the panel also do small tack welds and move around a lot so as to not make concentrated heat keep a body hammer and a wet rag handy cooling hot meal with a wet rag shrinks it whenever you do a weld you can tap it down with a hammer wile it's hot to keep the overall profile of the roof in check you won't always need to tho it's called hammer welding another tip is if you get in trouble and blow a hole in it you can hammer the end of a copper pipe flat like a spoon dolly and hold it to the back side of the hole and fill the hole in with the mig usually the weld won't stick to the copper it works pretty good