I'm not sure that this reply is going to be very helpful but I have used a vacuum-formed plastic product supplied by Garden Railway Specialists (of Princes Risborough). A large sheet includes two panels of corrugated iron, with boltheads and overlapping joints moulded in, each about 114mm by 400mm, that are just the right width for a wagon roof . . .How do people manage to get their corrugated roofs looking so good?
Interesting but does not show up on the site search I just did?B&Q sell sheets of corrugated aluminium. Possibly slightly under scale corrugations but it has the advantage of being available in large sheets if you have a sizeable roof to do. I just drew/painted a representation of separate sheets on mine, which looks fine at normal viewing distance. View attachment 280671