You can also purchase a shrinker/stretcher from Harbor Freight or Eastwood, and start making some of the main shaped sections. (90 degree bends, etc. Then Go back and template out the flat stuff, and weld it together. Use shop presses with Oak/Maple to help form the shapes that you need for structure.
I spend a lot of time hammering everything into shape from cutoffs of shapes that are relatively close, then surface finish them.
Structure is slightly different- It doesnt have to be pretty, it just has to be fairly accurate.
Dan