I assume you just want to keep the wood chips dry. I have a shed at my house where I store fireplace wood. The shed is 10 ft x 12 ft, and has a gravel base qbout 8 inches deep. The wood sits directly on the gravel, no problem since it is well above water table. The shed itself is supported on concrete blocks set directly on soil, not very elegant, certainly not suitable for a house foundation, but plenty good enough for the shed, which has been there since 1959 with no apparent problems. In fact, there used to be a horse in the shed, now it is full of wood.
I would not waste the money building a floor for the shed if you only plan to store wood chips, spend the money making yourself a nice big door so you can get the chips in and out easily, and build a solid roof to keep the chips dry. I also would not spend a lot of money on a foundation for a wood chip shed, concrete block with a PT sill should be fine if you fill the block with concrete and embed anchor bolts. Make sure the soil is solid underneath the block, if necessary you can dig out a foot or so so you can have a double block foundation.
You need to check first with the building inspector, make sure it is OK. At my house, the shed was built before there was an inspector, so nobody really cared.