I decided on a shape I liked (cub/modernistic), and using information on how to draw ellipses from Andrew's site, I drew a couple of profiles until I found one I liked, and I thought would work.
I transferred that shape to a full sized cardboard mock-up, and it looked like it would work, so I made a wood pattern out of a piece of MDF board, and started designing the rest directly on the pattern.
I realised real quick that I couldn't make it fit with a 4'x8' sidewall, so started all over on a 4' x 10' sheet of particle board. Been designing as I go, and other than my notes and marks on the pattern, I really don't have a plan.