It appears to me that i can buy used racks like they
have in home despot cheaper than i can buy new steel for. I had the idea
of putting together a box useing that suff like an erector set. I would tack
weld the joints and cover it as you suggested. Am i barking up the wrong
tree here on this or you think its a workable plan?

I am in the final touches of doing something similar, though I also am
operating under different constraints. I can make anything I want
without a permit as long as it's 120sf or less, and under 35' tall
(!). I found 4 15' uprights and a couple dozen 8' load beams on
craigslist. I would have preferred 10', but this was what I found
without paying twice as much.

With the uprights, the outside length for a pair was 8'6. The metal
siding I found has a 1-1/2" profile (I would have preferred r-panel),
so that made my total width 8'9, divided into 120 allowed me just over
13'6 for the length. With these materials, I would have preferred to
be able to build a foot longer, as it meant the beams I used to span
between the two racks (ends of the shed) had to be cut down a
foot...but I have a buzzbox and a pile of 7014, so all it cost me was
time. I cut the uprights down to 10' to minimize the madness a
little. 12 or 13 would have been nice to allow standing in the
"loft".

I grabbed some metal studs to build out a gambrel roof, with the
center ridge being a chunk of S8 with a hoist trolley, up on welded
brackets. If I had enough sheet steel to do the roof, I'd have just
added a couple of parallel purlins at halfway between that and the
corner, but instead I used rafters, OSB, and the same shingles as I
have on the house. There's a 2' stickout over the 5' wide sliding
door. All the offcuts from the uprights (except for some of the x-
bracing) have gotten recycled into other parts of the shed. The
bumpouts for the gambrel look like they'll be nice shelves.

So yes, I think your plan has possibilities.
--Glenn Lyford