I want to put a metal roof (the plain, wavy, 8' x 26" panels) on a cabin which right now has a shingle roof. The existing roof has a couple of leaks. I plan to nail the panels right over the shingles. The roof is exactly 8' from the high point at the top down to the eaves. Questions: The nails that I plan to use are 1 3/4" ring shank neoprene washer hot galvanized roofing nails. Are these good? How much overlap between panels do I need? They make rolls of putty-like stuff that is supposed to go between the panels. Do I need this? If I do it right, will the roof not leak when I'm done? Are there any questions that I should be asking that I'm not? Answers to any or all questions, or any other information, greatly appreciated.