there are books available thru interlibrary loan at your library.
I read the oldest one there. At that time....1995... there was one.
I figured aluminum tube welding.
There are hands on courses..one in Portland.
In your garage the process requires building wooden jigs for holding tubing in line at the correct angle. Jig building is probably impossible for the average handyman. or a very slow process. Thus the courses where there are jigs on hand.
Try rebuilding an older quality frame to 21 Century specs I did this with a 20 year Raleigh and brought a frame for a cyclocrosser trekker build.
Buying all parts during sales the R cost 800 with wheels n the cyclo with frame cost abt 1300. I ride believing the ride is mine tho I did not weld it together.
The parts do not bolt on. Modification n adapter plated need be made from aluminum n mounted.