Every Friday (except those that fall on official holidays), Chabot Space & Science Center holds a telescope making workshop. These workshops have been happening since 1967, and you don't have to attend a continuous series to learn how to make one.
Whatever stage your telescope might be in -- whether just an idea, or a nearly finished project, bring it in and the experts at Chabot will help you turn it into reality.
Keep in mind that while a telescope made here will cost some money, it will be about half as much as a commercially bought one, and will probably teach you twice as much about how telescopes work.