I'm looking at purchasing a 3 bed semi, which has a garage built on the side. The garage has a pitched roof. I am thinking of purchasing and building a new extension, knocking down the garage(as only single layer brick) and having built a garage with room above it. How much is this likely to cost? I know how long is a piece of string but just a ruff est wud do? Garage wud b of standard size, with same size room above it.