I don't think I've ever seen one "single" source for observatory blueprints and support contractors. Usually, you have to decide what type of observatory you wish to build then select a manufacturer who will work with you on design specs and possibly provide recommended contractors. For example, Ash domes can provide a specialized crew to assemble their domes on your site. Other companies, such as PierTech, can provide you with blueprint specs so you can mate their ROR components to an existing structure using your own contractor. Some small firms can custom build an observatory but it's mostly dependent on where you live. In either case, unless it's a custom structure, you'll need to refine what type of observatory you want to build (dome, ROR, etc.) then contact the various vendors for more details. There are lots of online and publication resources that you can use for planning. Here is one such source for things to consider when building a dome:
And there are books that provide helpful hints at building ROR structures:
Edited by John Carlini, 23 July 2020 - 04:24 PM.