Hi & welcome. Let me see if I this right. You have a metal roof nailed directly over a shingled roof?? JD is our roof expert, but I can honestly say that I have never heard of doing it that way. That is not to say it would not work, just that I have never heard of it. I'm sure JD will see this and add to it.
As for a manual, Mark, the owner of this site has written a book that covers about any problem you will ever encounter, it is written in a generic form. I highly recommend it. Greg
"If I can't fix it, I can screw it up so bad no one else can either."