I took the frame building class offered by
The Crucible (Art of the One-Speed: Building a Bicycle Frame) and found it very worthwhile. Unfortunately, it's a 10-week class so it's geared towards people who live in the San Francisco Bay Area. They require previous welding and machine shop experience. For $670, I'd say it's a bargain compared to most of the frame building classes I've seen. I'm still riding the bike I built in the class on a daily basis!