I started by doing some "CAD" - Cardboard Assisted Design, that is. I made a few sample decks using some cardboard, and trimmed them until I found a size and shape I liked.
I considered cutting the deck out on the bandsaw or with a hand-held jigsaw, but decided I wasn't steady enough to pull that off. Besides, I have access to TechShop's Shopbot, and it's way more steady than I am.
Step 1: Sketch design on cardboard
Once I settled on a design, I translated it into the computer version of CAD, and then created the shopbot file from that.
Shown here is the test piece made from scrap plywood.