I don't know if this will help you out or not, but this is a tip I heard a long time ago about proper perch size:
You want to make sure your birds feet are wrapped around ~75% of the entire perch circumference.
You will also need to be wrapping the perch with something (someone mentioned vet wrap) to keep them from sliding, so that may augment the circumference somewhat as well. With that being said, the ones you are going to be using for perches should be able to meet that criteria, and I would personally use PVC pipes that are at least 40% larger for the structuring of the stand to ensure the stability. The taller you make it, the larger the pipes you'll want to have near the bottom, most likely.
I've personally never made one of these myself, but have envisioned them and done research. Have you tried drawing up any technical drafts or blueprints for what you want to do?