We used "used" corrugated metal on all our chicken houses. Because of the previous "holes" from the screws I filled them all with Lexon (sp?), which is like liquid nails or caulking. Then we used the typical sheet metal screw with the fancy rubber gasket on it for a good seal. If you tighten them too much and squish the rubber gasket, it will leak. I had several leaks and just found them when it was raining and marked the holes and when dry I but more Lexon or a new screw. The I discovered that rain was coming around the wavey part of the metal where it attached to the roof beams, so I put that spray foam insulation in those. I also had to caulk one corner on the outside of the coop because if it rained hard and fast it would leak there. It has just been a fix as I go. I also have external nest boxes which leaked. I tried to fix them several times but ended up putting a piece of left over linoleum on top. Doesn't look pretty but its functional and no leaks. I hope my experiences help you out some. Just fix what you have, plug all holes and build bigger and better next spring/summer.