i plan on building my own 12'x12' wooden shed in my backyard for tools and lawn chairs etc.. I am pretty proficient at carpentry and woodwork, but i have never made a freestanding structure before, so i know nothing about foundations.

for the foundation, i don't want to use concrete (too expensive and a bit overkill), but i want to make sure the shed is sturdy. i want to use 4x4 or 6x6 pressure treated timbers for a skid and then put the shed (with a pressure treated plywood floor and 2x4 joists) on top of the skids.

the main question i have is...do i need a gravel base under the pressure treated timbers even though they will be also treated for ground contact?

I have read so many opinions about this, my head is starting to spin. which is why i am turning to the reliable, cool heads on gardenweb.