Not sure what you are asking.
For me I usually sketch out the scope dimensions using the manufacturer specs for tube and length and diameters, then measure the base and prospective rings. By sketching it all out you can determine if it will fit or not before you start trying to assemble it.
Without knowing what you want and the details of what you already have we can't steer you in a helpful manner.
I guess I get that method from the engineering side of my brain. (Not an engineer by training, but I sure engineer and build a lot of things)
I hope that makes sense and helps.