First DH built a wall 1 block high all round to stop rain water coming off the hill at the back and into the shed. Next the cement mixer arrived and DH and DS got their wheel barrows into action. Then the concrete needed tamping down to remove any air bubbles which would have left holes when the concrete dried.
Between them they shifted 2 1/2 cubic metres of ready-mix concrete!!
You can see the old shed, its the green bits to the left of the pink garage. It has a door leading to a triangular space along the back of the garage, and the corner of the garden. This is what is inside it:
complete with most of a small car, and rats nests. So we took it down
most of the side triangular bit gone, and the nasty plastic roof