Just to throw out another option,
I've built 2 sheds,
First I did on concrete blocks with PT 2x with CDX plywood. Was a pain to level the blocks, it raised up the floor so it sat taller, and needed a bigger ramp and when I added up the cost and the PITA effort to level the blocks in my yard, when I built my shed in my new house I did it differently.
I paid to have a concrete pad put down with anchor bolts. it cost more, but i didn't have the need to do any of it myself, deal with the leveling etc, and I'm happier with the finished product. I also had him pour a little ramp up to it.
Now the nice gentlemen who did this poured it out of square...which pissed me off on such a small pad of 10x12.. but I still am happier with the shed.
I also had all the lumber delivered along with vinyl siding, and roofing material etc, to save myself time and effort for all that crap.