20 x 14' shed

How wise is it to build a shed without a firm foundation, but to make a raised frame with legs and concrete them in like fence posts?

I could make a foundation, but the ground is extremely unlevel and the size of this shed means it would cost a lot, and take a while to lay down and get level.

The floor (probably chipboard) would be supported by 2x4 joists going across the 14ft length, at 2ft intervals, but instead of being on the ground they would have 3 supports - one at each end and one in the middle.

cheers,
Gus

I lay concrete blocks on there side, spaced apart with bearing timbers.

perfectly reasonable way to do it, but you will be better using 6 x 2 joists at 400mm centres.

I built a 20' x 10' shed (well, still doing it) The floor was laid on plenty of breeze blocks side-on. Bits of membrane on top of the blocks. "Joists" were scaffold planks flat on the blocks, and the floor was scaffold boards across the "joists". The floor boards are screwed to the "joists", and the shed framework is screwed to the floor. Three years and it's fine.