I saw a program recently, I can't recall the name, where the police busted a guy with exactly the same setup you are talking about. He had a dumpy looking shed on top of a beautiful basement all fitted out with growlights, heaters, and half a million dollars in pot. So sure, you can put a shed over a basement.
As to cost, I don't do cost, ask a local contractor.
As to your cement computations, you need to be a little careful about terminology. You are probably talking about concrete, not cement. If you go to the local material supplier and ask for cement, you will get bags of Portland cement, which is one ingredient in concrete, the other ingredients being sand, aggregate, and water. Concrete is not calculated based on square feet, it is sold by the cubic yard if you need a truckload, or is mixed one cubic yard (usually just called a yard) at a time in a mixer. Or you can buy bags of premixed concrete, just add water, mix, you typically get one cubic foot of concrete, 27 cubic feet to the yard, per bag, but there are different sizes of bags, they all say right on them how many cubic feet of concrete they make.