You should start with RESEARCH. Research the various type's of telescopes, and the lenses needed to fabricate them. Find one that uses optical components similar to them materials supplied. Research the optical formulae associated with them. The best way to solve a problem, is to learn of the various ways that have been used before. If they are not perfect for your application, they will at least offer a good starting point. If all else fails, EXPERIMENT!!!. Many engineering advancements are made through simple hands-on experimentation. YOU CAN DO IT!!!!