Today was spent constructing the timber for levelling: side rails and the tamper. Firstly, I attached a length of 1x1" timber to the side walls to provide a platform to level off the concrete. I borrowed a laser level to help to ensure that each side was in line. This made the job quite easy. After that I made the tamper out of two 1x4" timbers sandwiched together and screwed. I cut a slot across the ends that locate onto the rails such that the when resting on the top inside edge the bottom of the tamper hangs at the 100mm level for the floor - I'll try and get a photo to describe this better before the concrete goes in.
Next I used my hammer and bolster to break up the square section paving edges I bought from the builders merchant, see earlier. These are 2" thick and will space my #142 mesh centrally within the slab. The mesh will just rest on top.