I have an old barn about 80 years old. The roof has one layer of cedar shingles and one layer of asphalt. Can I go over the top of these again. I'm worried about the weight. Can I put a tin roof over the top. I don't want to tear it off if I can help it. I have hay in the barn and tearing it off would cause a lot of loose nails in the hay. What about rolled roofing.