I consider myself a proficient welder/fabber, but am look for an exhaust kit. I have a truck lift, mig and tig welders, and most every cutting tool out there. I don't consider making my own exhaust to be a bargain.
First of all, you would need to order a downpipe from somebody. Then you need a fitting to go to 5 inch, and then you need pipe and elbows. Custom bends can be made by bandsawing 90° elbows into different angles. Then weld it all up. Then make hangers. Doable, but not cheap and fast either.