When teaching banjo history as a way to discuss race in America in my classes at Bowling Green State University, I have had the opportunity to bring them to the arts area and build banjos from scratch.
To make this work, I prepared two guides. One was for a few students who were working independently, another was adapted for a larger class. I share them here with the hopes that (1) you might make some banjos and (2) you'd let me know how it goes!
I do some things differently now than what these guides share, but they will get you up and running.