For my final OpenSCAD project, I did a diamond ring. It took a while to know what my design was going to be of, but then as I looked back at my twenty objects, I saw that they looked like bits and pieces of a bigger object, and one reminded me of a diamond, so I decided to go with the ring.
It actually took a lot more coding than I originally thought it was going to be, but I am very satisfied with the outcome.