I always seem to have the need to add another shelf to the garage or shed. Strong metal Home Depot brackets cost about 7 bucks and the junky ones around $2. Seems like I need a tonne of them. Being in California where basements are rare, all of our storage is in the garage. So I sketched up a bracket that can be cut on the ShopBot. It works out to about 87 cents per bracket if using a $45 piece of 3/4" plywood and a bracket that is 12" x 8".
When I am working on other ShopBot projects and often have some scrap so I drop a couple of these brackets into the drawing to make use of the excess wood. That way, I always have a stash of brackets and cut down on my scrap too.
You'll see in the photos that I attached some 2x2 strips to the drywall on my garage at the stud locations. This was a tip from the Family Handyman magazine. These strips allow my brackets to be quickly installed by screwing from the side, as shown. The 2-by's can accept any type of custom bracket that you can come of with for holding tools - like weed whackers and sports equipment. The shelves are fastened to the brackets from the top with screws.
These are incredibly strong. I sat across 2 of them (170lbs) and they didn't budge. The brace that goes between the horizontal and vertical member is obviously the key to the strength. The drawback is that it impedes shelf space on a shelf below. So you can play with the position of the brace - move it inwards for more space and less strength, depending on your needs. Scale the drawings for larger or smaller brackets, of course.
I included a dxf for a 12x8 bracket for importing and a jpg showing the layout for piece a 48"x24" plywood. I can fit about 13 of them. The zip file contains a .crv (Vcarve file) with the layout for a 48"x24" sheet.