We just found this dip in our roof that it causing rain water to leak through the wood directly under it. (It covers an open patio, not interior living space.) We'd like to make the repair ourselves instead of hiring a roofer, but I'm not sure where to start. The roof has asphalt architectural shingles and we live in the northeastern U.S. where we get a lot of rain, snow, and wind. Basically, our roof takes a beating so we need to make sure the repair is sound and will hold up in nasty weather.