This is more or less what I did for my 10x16 shed, but I'd argue the gravel doesn't need to be that deep, and you don't need to bother with the different gravel types. Just get a couple yards of 3/4 crush, nestle some pavers in, level them as best you can, and call it good. If the shed settles a bit (which it will), the worst case scenario is that the doors stick. When that happens, jack up the corner that settled with a floor jack, stick some plastic shims on top of the pavers, and drop it back down. It's a 5 minute fix.