Building a bass 8 by 3.5 metres. the depth of the bass is about 150 mil, ive layed down all broken rocks bricks etc on this. How much sand/cement do i need to order?

You have approx 28 square metres at 150mm deep your looking at about 4.2 cubic metres of concrete. Thats going to take some knocking up if your doing it by hand. My suggestion would be to order in some ready mix, get a couple of helpers on the barrows, you will have it down in no time. Make sure you compact the hardcore first, blind it out. lay visqueen and maybe some mesh. If your doing it in the hot weather, sprinkle it with water when starting to set and lay some damp hessian over.

hi for that quantity listen to BJD readymix is the way to go we find its best to use a barcher lorry which batch and mix the concrete on site so mix the ammount you need