Hi Geoff. It just so happens that I've done this exact thing. I had the slab poured inside the shed. The main consideration was to put a barrier between the concrete and the Colorbond because I was advised that if they were in contact it might cause the Colorbond to rust at the bottom. We had plastic sheeting under the concrete and ran this up the sides of the shed far enought to create a barrier, then trimmed it back later. There was timber formwork as well.
This worked perfectly. There were no issues and no rust subsequently. I'm no expert but it has been a good solution for me.
Done 2 sheds at home with concrete, didn't use plastic and have had no trouble with the galv sheets rusting, rails is something else termites have had a field day on some of the bottom ones. Cement both sides has kept the walls in place.