The cost of a new roof depends on the design of the roof including pitch, cuts, and obstacles such as A/C units. Other factors are the difficulty of removing the existing roof. For example some houses have multiple layers of roofs which require double the work and hauling. Obviously the most important factor in costs is the materials you are going to have installed. For example a roof with 15 yr felt paper and 15 yr 3-tab shingles is going to be cheaper than a roof with peel and stick underlayment and 30 yr designer shingles. You really need to determine what type of roofing system you want and speak with a licensed roofing contractor so they can accurately measure and estimate your roof.