deck blocks are ok, be aware you'll have to build a ramp for the shed as itll raise it up quite a bit.
Heres the one i built:
Advantages from self building
1) price, was about 1000 buck in materials
2) Customization (taller walls, i put a 3 foot overhang in the front as a rain shelter), sturdier materials (as i was planning to put a 2000 lb tractor in it originally)
3) Style, you can match the colors and trim to your house if its near it, or as i did, make it natural colors so it blends into the woods
Disadvantages
1) Time, it just takes longer
2) Tools, i had everything i need, but without a framing gun it would have taken a lot longer.