does anyone have any idea how much per SQ metre an extension would be - just for getting the shell/roof up for a double storey? (excluding electrics / plastering) i've seen 1000-1500 per SQ metre quoted but those seem to be quite old threads.
I think you can only use psm costs as a guideline as there are fixed costs which are irrespective of size. i.e a digger is usually hired by the day or week. If it's a standard 2 storey (no clay soil or drainage issues) I think a 2 storey extension is around £40-50k. It does seems to depend on where you are as the south east and London are considerably more expensive.