I'm pouring a 6x6 4' slab to sit a jacuzzi on. It won't need to be pretty or anything but I just don't want it to crack and break from the weight of the hot tub. I'm guessing I can rent a mixer and do this myself. I know how to set the forms but I'm not sure how much material I would need (like sand, cement, etc) Also, what should be on the ground? A sheet of plastic, rebar or a small 1' deep bed of pea gravel? I would apreciate any help, I'd like to do this one myself if possible.