Felt paper, also called tar paper, is simply another barrier between the inside of your house and the elements. It is impregnated with a water-repellent substance. It comes in rolls of varying widths and lengths and is chalked with lines at certain intervals. The lines are primarily useful for confusing the roofer when he begins to lay down shingles.
Felt paper is one of the most dangerous substances known to man. It has a tendency to tear easily. At the same time, it is exceptionally slippery. This means, when you walk on it, it can tear loose and send you sliding toward the edge of the roof. You are never so aware of your own mortality as when you are riding an express piece of tar paper to hell...or to heaven as the case may be.
I love tar. This gobby material will cover a multitude of sins. It will seal holes, cracks, seams and punctures. It will adhere to every material known to man. It is pliable, and it will stay fresh in its can for years.
Tar, besides being useful, is pervasive, (meaning, it gets all over everything). Every time you dip your putty knife into the tar, you will get a little on your hands, this migrates to your face, clothing, and every tool you touch. If you happen to own chickens, it is best to stay away from them for a few days. You do not want to learn firsthand why tarring and feathering was such a popular method for dealing with tax collectors in the 18th Century.
Roofing nails are a commodity you can never get enough of until you have too much. It is impossible to estimate exactly the amount needed. Running out of nails while working on the roof means suspending operations for a hardware store run. Too many means you will have to find storage for a huge box of nails.
Like tar, roofing nails have the unfortunate tendency to migrate. If you store your nails in any proximity to an inflatable item, you are asking for trouble. It is best to store them in a well-sealed vault in a corner of the garage and under strict guard. Ask any professional roofer how many nails he has found in the front left tire of his pick-up truck.