Well evro once the walls are on i have to dig out the dirt and the concrete is poured in the shed walls will hold the Concrete in shape and make sure no water can get into the shed. Unlike if you build the shed on
top of a slab
You're not serious ? you can't be ...
I have a 30ft x 80ft shed and this is the same method I used.
I finished building it about a foot off the ground, bobcat in heaps of 10mm blue metal till about 100mm from bottom of sheets, compacted, layed down plastic, put in reo, on barchairs, tied together. layed the slab about 1" above the bottom of the sheets.
Has been up for 6 years now, no probs with water as it is built up off the ground so water cant sit around rusting the sheets out.