I’ve been more and more interested in this lately and have heard, or thought I’d heard about courses available where you can learn to build a frame.
Do you want to build one frame, or do you want to learn to build frames?
For the former, one of the courses like Dave Yates’ one is perfect – you spend a few days doing fun stuff and end up with a frame you can ride.
For the latter, maybe a course but perhaps better to go on a brazing and metalwork course at a local college, then spend all your spare time practicing.
You can learn the basics of building a frame in a weekend – getting good at it takes a bit longer 😉