I want to put a chipboard floor in a building 13m x 4m that already has a sound concrete slab but with a slight run-off and a 6 inch step running the length of it down the middle. I'm not too worried about keeping the split level. Can I even up the floor by laying something like 4x2 on a dpm and then screwing the board onto it? How much insulation would I have to add and is there a minimum void? Or is there a better way of doing it? Any help would really be appreciated.