I like 04Chase's setup in post #12, seems about the right size for what I typically have around.
I just moved and ended up letting most of my scrap go, but I did keep some. Now would be a good time to build a rack of some sort - before I collect a bunch more.
I worked with a guy who had another kind of storage rack which I am also thinking about making.
It was a 2'x4' (approximately) base on wheels with an expanded metal floor.
Then on each end was an 'A' frame and a third one about a foot in from one end. The 'A' frames were probably a little shy of 4' tall, but they could be made higher or lower.
There was a piece across the top connecting them for stability that was also a shallow storage pan, about 4" high and maybe 12" wide that ran the whole 4' length, it had an expanded wire bottom so it would drain if necessary.
It would hold anything under a foot or so long and was at a handy height to sort through small pieces.
The 'A' frames had ears sticking out which were about 6" long and made of heavy pipe with caps - could probably skip the caps, but they helped keep stuff on when rolling the cart.
Each side had 4 rows of these 'ears' so you could have 8 places to stack different materials, pipe, box channel, angle iron, flat, bar stock, round stock, etc....
With the center 'A' frame closer to one side you could rack anything over a foot or so long on one end, over 3' could go toward the other end, and 4' or over could go anywhere.
Less than a foot went above in the shallow pan - which you could make larger, or put one on each side or whatever depending on what you keep.
Inside the 'A' frames you could keep sheet scraps of pretty good size, this particular version wouldn't quite hold anything over about 3' wide on one dimension, but you could build the frames taller if needed. Might want to make the base a little wider if you did that though.
Overall a fairly compact, mobile way to store a lot of scrap pieces in an organized way that is fairly easy to get at.
The sheet stuff could be a bit of a pain to reach so if you do mostly sheet work with some long stock it might not be the best solution. But it you keep mostly bar/flat/box stuff and a little sheet it works well.
If you did more sheet, I see those carts like they have in Home Depot/lowes for sale on Craigslist once in awhile. If a guy put 'ears' on the side of one of those for some long storage, and welded a shallow pan on top, or one on each of the shorter end bars lengthwise and have pretty much the same thing (about twice as big though) but aimed more toward sheet storage.