Just finished my first custom handle for comp climbing. I started with a set of aluminum tangs from a pair that I ordered from Dennis at Vertical Life in the Netherlands. I bought a pair very early after he released his first run of handles and unfortunately I broke the 3d printed cheeks on them very quickly as I used them unwrapped and on real rock (which was not what they were designed for, so my bad).
Took a lot of inspiration from custom knife handles and made my own micarta out of thrift store denim and epoxy. These were cut and shaped by hand but I have plans to experiment with some designs to be cut out on a CNC for other purposes.