Sides: 1/2" plywood - hardwood (Luan) or birch would be best, but any kind of plywood will do, maybe even 1/4" would be OK
Shelf back: 1/2" plywood, since that is what we had in the garage, but 1/4" or 1/8" thick would be fine too.
The following pieces are all simply cut to the same length. We used 19" to fit the room, but you can use any length you want.
(5) Shelf bottoms/tops: 1x12 pine
(4) Front edges:1x4 pine
(1) baseboard 1x2 pine
Step 1: Cutting the Sides
There is a gap where the front boards meet the bottom ones. I did not worry about it too much, since it's on the underside of the shelves. I note it in the next step, but I did decide to bevel the front pieces a bit with sanding, and with that, the layout of the template changes slightly. You could also try caulking the underside or something - I just wanted to keep things simple to make.
The approximate heights of each of the shelves is:
top shelf: 41"
shelf 2: 21.25"
shelf 1: 11.5"
bottom shelf: 2" - this one rests on top of the 1x2 kick board
Sorry - I did not measure the angle of the front boards - it looks like about 45 degrees from the picture.
Step 2: Horizontal Pieces and Assembly
Once those pieces are cut, assembly is very simple - I used 1 5/8" drywall screws from the sides into the shelf - no rabbets etc. I used a pilot hole, then painted over the screws, but for a more finished look, you can use a counter sink pilot bit and wood putty to cover the holes. Be careful not to drill too deep - the sides are not very thick, and the screws will sink in a bit naturally anyway.
I added some felt pads on the bottom to make it nice on the wood floors.