I had a tree fall into my roof this winter, and it made it leak to the point of ruining my drywall. My home was constructed in the early 20's. I would like to install a metal roof, but there are some waves in it (if you know what I mean) can I fur it up before installing the roof, or should I just go ahead and re sheet it first. as you may be able to tell, I am in the first step of this whole roof thing. I am doing it myself.