Can anyone on here advise how much a single storey extension 4x3m with pitched roof, x2 velux and bifold doors to a plastered finish should cost me roughly? I have had a real mix of quotes, varying massively, with even as much as £20k between them. I have been really shocked as I didn't think a single storey extension of this size could cost so much, and prior to going ahead with plans I was told it wouldn't be that much. If anyone has any builders that they would recommend that would also be apprecited!