Real framebuilders are working to fit anyone, against a backdrop of everything. When you design a frame for yourself, you are working with one person, and presumably some known preferences and real world parts. Presumably you are serious enough about your riding to have your position worked out, and all you have to do is model that, or make some subtle changes if you think the structure can be improved, or are moving to some different parts. For instance a seat post with a change in offset.
If in addition I was planing on a frame from a style that I was not familiar with, I would probably look at current models for general info, though if one is making a classic there are probably reliable rules of thumb in Paterek.