When comes to roofing there are four elements that make up the cost of taking the old roof off and putting a new roof on. The first is the most obvious but it must be said, The size of the roof takes the majority of the cost. If you have a large area to cover this will obviously cost more than a roof with a smaller area.
The second is the angle of the roof. The steeper the roof the harder it is for the roofer to carry, move, cut and install a product. The angle also create the opportunity to cause damage. your old roof is quite heavy and with a steep slope to slide down the shrubs and plants could see there final days. extra protective equipment is available but this is of course an additional cost.
The third way to pay more is if your roof is cut up. What I mean by that is that there are a lot of hips and valleys. Why this cost more is the more cut up your roof the more wastage. More product is ordered because after the roofer has cut up the shingles there is a high amount of waste that cannot be used.
The fourth has nothing to do with the roof but with the terrain around the home. If you live above or below a very steep driveway or maybe on a rocky terrain it does take more time to change your roof. More time means more cost. The roofers are not expected to get paid less when the job is harder to do. They get paid more!