I second ace's advice. I hired a professional stunt coordinator for my last movie and that's exactly what he did. He bought boxes from U-haul so they'd all be the same dimensions, taped all the seams and stacked them into a cube shape, then placed mats on top for good measure. Worked great. He did the stunt twice.
To OP:Not to discourage you from posting but u can usually find what your looking for with a quick search first. i myself start with google, then search forums, then start a thread.