Can you use siding on a roof with a normal pitch, instead of roofing materials?

We are putting a new roof on our garage and doing the work ourselves. We want to put on a metal roof as we did on our house a few years ago. However, I would like to find something more decorative than just the plain metal roof, since the garage & roof are in close proximity to our deck and is very visible from the house. We looked into the new metal shakes, etc., but they are very costly. So before we just give up and go with the plain metal roofing sheets, I was wondering if we could find some decorative siding (vinyl, etc) and put it on the roof instead of the sheets of plain metal roofing. The roof will be going over an existing shingle roof that is starting to lose a lot of it’s shingles. Would the siding be able to shed water, snow, etc. like a metal roof would? We live in Indiana. What do you think?