How do i know how many bundles of shingles i need for my roof?

both the above answers are correct, just not complete. You need to also account for the starter shingle (this one is facing backwards along the drip edge) and the ridge cap. Now depending on the type of shingle used, will determine some of this. If you are using 3-tab shingles, then the same shingle can be used for the entire roof. However, if you are using architectural shingles then you will those for the roof plus some 3-tabs for the starter and then enough hip/ridge shingles. Hope this helped. If you need further istance you may contact me directly.