I price by sq metre, because i started off giving a price I thought I'd get or was fair just to get the work and a start to get me noticed. The problem was when being asked to quote for a referal job and I said say for example £95 the customer said Oh mrs smiths seemed bigger than mine and she only paid you £85. So I decided to be more proffessional, granted after an ear bashing by my sons, and price per sq metre to get a baseline to work from, then adjust as req IE surface type, access, drainage etc;