Damp proofing shed base built on a slope

I want to build a large well insulated shed (to house a tortoise). It will be a self build because of the unusual shape to fit where I need it to go. The base will be concrete with an air gap, then insulation, then air gap with a wooden floor above. However, because it is being built on a slope, the floor level at the back of the shed will be about 70cm under ground level. I will build a block wall for the parts of the wall that will be under ground level. What is the best way of damp proofing the underfloor area that is below ground level? DPM under the concrete base and up the outside of the block wall? Tanking the inside of the concrete base and block walls? Other suggestions? Thank you.