I love to make things for myself, but in this case...these frames aren't so expensive. By the time you buy what you need, i.e. spend the time going to the hardware store, thread the pipe tight enough to where the joints don't slip, or weld it, assemble everything, get some foam, paint it???
Besides. Wouldn't use 3/4 inch pipe. Its not rigid enough.
Just my 2 cents worth and food for thought.