While I have not completed a similar search myself I would expect that creating a "custom" scope is like building a custom anything...
Although there are a number of fabulous handmade/handcrafted professional scopes available they are not "custom" made and will be built from "similar" materials and to a defined pattern...changing the "pattern" could quickly add up...like many, I am curious as to how you go...
Someday I too will move to a slightly bigger scope but I want to keep my feet on the ground...Based on that fact I reckon 15 inches will be about my limit...maybe something a little bigger can be done with a very fast mirror but that "project" is a ways away...
Good Luck!
