According to our roof installation cost estimator, the average price to install or replace a roof is $5,951. There are many factors that influence the final cost of a roof installation. Many of them vary over time and across locations, making them difficult to predict.For this reason, there is a wide range of possible prices. At the high end, people pay as much as $11,000; at the low end, they may pay as little as $3,000.nless you have a flat surface for a roof, your roof has a pitch. As you might expect, pithed roofs cost more than flat roofs. Not only do they cover more surface area (more materials), but they are also harder to install.