We are looking to buy a house and have found one witch has planning permission. But I have no idea how much to estimate... it's tiny at the moment but has planning for 6m rear extension + over the garage. We would need to also do a loft convention eventually to fit our family comfortably... it also only has a upstairs bathroom at the moment so ideally adding 2 bathrooms as well.. anyone done similar work that could give me an idea?