For HO scale corrugated metal I got a piece of plastic .040 corrugated metal and use it as a mold. Put a drop or 2 of dish detergent and add a little water (to release the surface tension). Then add a generous amount of Elmer's glue (PVA) and wait for it to dry. Then add another layer on top and wait for it to dry. Then CAREFULLY peel off the glue layer and paint it as you would any corrugated metal. For O scale corrugated metal I got me one of those toothpaste squeezers from Amazon (only $9.99) and save every beer can after I drink it, cut it up with my tin snips and run it through the toothpaste squeezer. Now I've got more O scale corrugated metal than I know what to do with. I guess from now on all my scratch built O scale buildings will have corrugated siding and corrugated roofs, LOL! Cheers from eastern TN