Got a small outbuilding. It’s about 3.5 x 3m. We want the roof raised, internal wall removed, one door removed, roof replaced with fibre glass and a little porch put on the remaining door which will be PVC. The floor will be raised and everything will be insulated. It’s a home office. Builder says £18,000 🤦♀️😬 Seems like a lot to me. Surely?