Here's a shot of the main shelves in my shop (er, basement ;). I started by placing eight 2x4s along the concrete wall. They're long enough that they extend up next to the floor joists for the floor above, and screwed them together. Since I used manufactured I-joists, I bolted a foot long section of 2x4 to each joist's web in front of each shelf 2x4. The purpose of all this is to provide a great deal of strength that prevents the 2x4's from falling away from the wall - there's no need to hold them up, since they rest on the concrete floor.

Once the uprights were installed, I added L-brackets for the six shelves (that's 48 brackets). I used the 12" brackets, which are really something like 11.5". Start at the top! They overlap each other by 1/4" or so. I used three 2" #12 screws, with the two top ones angled towards the center of the 2x4 (since the holes are almost 1.5" apart).

The shelves themselves are pre-made MDF shelves, 12" wide and 8' long with the bullnose alread there. I got them at Home Depot. 3/4" #6 sheet metal screws hold them in place.

I soon realized that the 3.5" gap behind each shelf was really a bad idea! So one week I spent the odd free minutes making fillers for each - 42 of them. I glued & nailed (brads) two 1x3/4 scraps to the 2x4 just under each shelf, and nailed a 3.5"x14" filler on top of those flush with the shelf. Effectively, each shelf is now 15.5" deep.

Hints

Next time, I'll use SBS brackets from Simpson Strong-Tie.