I have been an amateur builder for about 26 years with 14 frames built . I learned on my own from a Talbot book on Frame building published in the 70's. The brazing part I learned quickly. I never had a frame fail, but alignment ( IE; not having to bend the she-it out of the frame after brazing) and the cosmetic details took me about 4 frames to get right. each successive frame I have learned something new or improved my technique . The last couple of frames (years 2006 and 2007) I finally got the paint work looking the way I want.

IMO if you have good mechanical aptitude and have the patience and desire to learn on your own it's very rewarding. On the other hand if you want to go the school route you should be a couple or four frames ahead in experience.