This is really take two- I did a paper prototype of this yesterday (http://www.instructables.com/id/Rapid-Prototyping-with-Paper-T-Shelves/). But after messing around with my little triangles-and-squares glued together model, I had to admit to myself that something was structurally wrong with my model. So I went back to the website and, with the help of my friends, realized how it was really supposed to be done! It's not tiny squares and triangles; it's bigger triangles with slots to fit them together!
I've really been enjoying working with the easy geometric shapes, so I thought I'd make a step-by-step so you could play along.
Step 1: Cut out triangles and slots
Above is the design I used to cut- it makes 32 triangles, though I only used 19 in the shelf design I built. Basically, it's a triangle with two slots that go halfway through between the midpoint of each leg and the center of the hypotenuse.