First you need to decide how many items the display should contain, how much counter space you can take up etc. I played around a little with the product to make sure different colors were visible etc. After your concept design is complete, draw it up in your favorite CAD program.
For the material, I looked through the TAP plastics samples, and decided on the 1/8" P95 acrylic green edge with a haze finish on one side. It basically looks like sandblasted glass -- pretty slick-looking stuff.