Hi Sandra.

The volume of cement you require is 8 x 8 x ½ = 32 cubic meters. I do not know how much cement will mix to make this many cubic meters. Perhaps on the side of the bag it says something like "one bag makes 0.025 cubic meters". It would depend on the size of the bag and the amount of water you mix with each bag.

For example, if one bag, mixed with water properly, does make 0.025 cubic meters of cement, then you would need 32 / 0.025 = 1280 bags of cement.

Be aware that cement and concrete aren't quite the same thing. Concrete is a mixture of "aggregate" (stone, gravel, sand) and cement. This is what is usually used in floors. If that is the case, you will want to buy less cement and add aggregate.

Cheers,
Stephen La Rocque.