The price of your new roof depends on many factors. Among them are the type of shingle you want to use, whether your roof is considered "walkable," its square footage, the number of irregular shapes on it and whether the old roof will have to be torn off first. Prices can vary by region as well. To obtain an accurate estimate for the cost of your new roof, local roofers will need to analyse it. You can use a simple formula to get a rough estimate, and there are some online estimate calculators that can give you an idea of its cost as well.
Assess the "walkability" of your roof. If it is relatively flat, then it is probably walkable. If it is steep and angular with lots of deep corners and inaccessible nooks, it is probably not walkable.
Assign a square footage number based on its walkability. If you have assessed your roof as walkable, then use the value of 80p per square foot for your calculations. If you have assessed it as not walkable, then use the value of £1.20 per square foot for your calculations.
Write this formula: Approximate cost of roof = house square footage x 1.5 x price per square foot.
Plug in the numbers. For example, imagine a house that has a square footage of 3,500 and a roof that is not walkable.
Approximate cost of roof = 3,500 x 1.5 x £1.20 = £6,313.10
The approximate cost of a new roof would be £6,313.10.
Compare your calculated value with an estimate obtained online. In the "Resources" section of this article, there are links to a couple of online roof estimate calculators. Use these to obtain more estimates of your roofing costs to get a better idea of what the actual cost may be.