I used them when I moved our aluminium greenhouse. I dug out a flat area, put down a layer of pea gravel, then the interlocking plastic tile jobbies, then I filled the pockets with more pea gravel.
I was quite happy with the result for a greenhouse, I think if I was doing it for a shed I'd consider using paving slabs over gravel to provide a more stable surface. Getting them truly level took quite some time - but then I was working on a slope so digging a flat area wasn't completely trivial.
