I have laid a bit of concrete in my time, but this job is a bit different. I have just re-roofed an old garage/outbuilding. It is about 6.5m by 6m internally and has an old concrete floor that is sloping by about 2 inches over the width. The concrete is about 6 inches thick and in reasonable condition. I want to pour a new concrete floor slab on top of the old one to raise the floor level by 4inches at the highest point and 6 inches at the lowest. Should I use a DPC on the existing floor and pour on that or should I bond directly to the old floor and what preparation would I need. Do I need reinforcing in the slab? Would you try and pour in one go or divide floor into sections? Any other advice appreciated too. Thanks in advance.