Just built one for all my sheet goods. Started typing this out and realized I didn't take any pics along the way... (in my defense, it was over 100* and I was just trying to get done) I'll try to snap a few pics, but basically what I did was run two 5' long 2x4's parallel to each other, and then across the top I set 3 30" 2x4's perpendicular, one at each end and one in the middle (and a 4th on one end to keep small pieces from falling through). Then I attached 3 pairs of 4' long 2x4's to 8" blocks on the bottom, screwing the other ends together. I capped it with a 5' long 2x4 screwed down into the ends of the vertical pieces. 4 4" swivel casters from HF rated somewhere around 250-300lbs each are at the corners.
And then for non-sheet stock I bought a metal rack from Woodcraft (added a shelf bracket in the middle for shorts). The bottom left is loose so I can slide it up when not in use so the wife can open the washing machine. Currently has a couple hundred feet of square tubing on it for the upcoming mission project
I saw that rack from Woodcrafters, are you happy with its capacity and adjustability?