There goes that sick sense of humor again and I love it! Seriously, a metal roof will surely gum up the works, you'll just have to get the antenna completely above it and as close to the center as possible. You'd even do better up in a tree well above and away from it, bottom line is large metal objects in the area are notorious for distorting the radiation pattern often to the point of nulling signals completely.
I had my antenna way up in the clear on one house and reception was great, I moved only a couple of blocks and everything changed. The antenna was in the same position relative to the roof only this was a tin roof covered with shingles, I lost about 25% of the repeaters I heard perfectly before. Cat On A Hot Tin Roof was a book by Tennessee Williams but he didn't try to put an antenna on it.
