That's not a cover for sheetmetal. It was original equipment on just about every closed car until the mid-30's. Stamping technology hadn't advanced enough to draw an entire roof, so they were filled with padded inserts on wooden bows. I am assuming you now want to cover your lumpy sheetmetal with a faux insert? It could be done on your existing roof, but unless your waves are very minor you are still going to see them. It may even backfire and pronounce them even more.
I would suggest finding a donor roof with a similar contour and cut out the shape you would like for your "insert". You could cover it with padded vinyl, and it would be easier to handle and to stretch tightly since it will be it's own entity. It would also cover up your unsightly roof repair smoothly. Attach it with some stainless trim scews or something of the like and it would probably turn out ok...