If you have a couple of good workers and an average size home, you should be able to tear off your old roof, lay felt, and re-shingle in 1 day. Here's the catch though, you'll have to work hard and coordinate the delivery of your shingles. You'll want them delivered right after you get the felt laid. This is because you want to have them delivered on a truck that has a method of delivering them to the roof. This is essential if you are dealing with a two or three story building, but is even desirable if it's just a single story. The belt will bring the shingles up to you so that you can place them on the roof. Have several friends with strong backs and load the roof evenly.

Coverage

You need to calculate how many square feet your roof is so that you can order the right amount of shingles. For a standard Ranch Style Gable like we're dealing with here, measure along the rake from peak to eave. Round up to the nearest foot. Then measure the peak from end to end. Multiply those two numbers and then multiply that number by two. This will give you the square feet of your roof. Add a few extra bundles for waste.

Next we have to consider how many square feet is in a bundle and that will tell you how many bundles to order. Sometimes approximations are made like 4 bundles per Square. (A 'Square' is approximately 100 square feet) Here's an example:

Roof measures 24' from eave to peak. It measures 46' from end to end, across the peak. This gives you 2,208 actual square feet for the roof (24*46*2). If we divide 2,208 by 100 we get about 22. So the roof is 22 Square. If 4 bundles of our selected shingle will cover approximately 1 square, we'd need 88 bundles (22*4). In this instance, I'd order at least 90 bundles, possibly more. Not only do you want to account for waste, but you want extras in case damage occurs later and you want to replace a shingle or two here and there.