Right Ho

Foundations

900 deep
750 wide
33000 long (centre line)

equals
33.00x0.75x0.90 = 22.275 m3

Assuming the the 900 takes the foundations to the top of the trench and you want the slab to the same height and is 6inch or 150mm deep to the same level the slab works out as follows.

8500 long
6500 wide
150 deep

So 8.5x6.5x0.15 = 8.28 m3

Total conc. required for Found. and Slab = 30.56 m3

Your supplier should be able to work that in to tonne or whatever they supply it in and ask your builder what sort of allowance should be made for estimating terms as those figures are based on the calculations provided.

If you want I can send you a spread sheet with the workings on - pm me an email address if you're bothered.



Real rough drawing to check I have understood correctly.

Jake