root-over-rock

New here and wanted to start with my newest project; for background (briefly) I've loved the art for more than 30 years and had at one time a lovely collection, a house fire managed to kill off the majority of my trees and theft of my surviving spruce forest killed my desire to invest any more...

I want to make a root-over-rock; specifically, one with a geode. The rock isn't the issue; I have plenty of areas to search for the perfect geode. The issue is growing it. I am quite new to the art of bonsai, and don't know how to make one. What's the best way to go about it? Should I find a...