first of all go to
https://companieshouse.gov.uk and check out the main contractors finances it will cost you the mega sum of £2.00 to do this...
600 m2 of float and set @ £20.00 per m2 = £12,000.00
less materials @ say £ 4.00 per m2 = £3,600.00 = after material £8,400.00 you then sub the work out at a canny rate of lets say £5.00 per m2 that cost you 600 x £5.00 = £3,000.00
gives you a pre tax profit of £5,400.00
if you are a registered subby then you will pay 20% tax on this amount if not 30% so best senario is 20% so you are left with £4,320.00
OK so now im getting to the point DIVIDE THE £4,300.00 by 600 = £7.17 per m2 profit if you go in at £15.00 per m2 you make £2.17 per m2 profit IE £1,302.00
if you start to supply material you need to concider the vat you pay on them? it all adds up... refer to my other post about being an employer....
its not difficult but you have to register with
https://www.hrmc.gov.uk then become either a sole trader, partnership, ltd company and file your accounts... if you are going to get a lot of these contracts then go for it and become a registered employer or subcontractor however the profit on this job if any would not pay set up and or accountancy fees to keep you out of trouble with the tax man... been there done the lot mate... tell the guy labour ony and you will have no hassle