From reading a thread or two of people doing this, building their own trailers… You will need to treat it as a brick and mortar build in some areas. Call in the building inspectors as well as the health department. But this would depend on your area I guess and your health department. I would check with your local health department first before doing anything.
Yes all the proper local and state agencies will be talked to. However they can’t answer every question. Especially as to whether or not it’s worth it to build my own or buy something used. Plus they can’t offer me real live experience. They can offer codes that must be followed.
Start off by figuring out what type of equipment you want/need and then research the companies that manufacture the equipment. Obtain the spec sheets for the equipment and then lay everything out on paper. Obtain prices of new and used and figure your cost. Now that you are familiar with cost, you can compare buying a used rig to building one. Also consider… when do you want the rig? You may not find a used rig in time.
Personally, I build my own stuff because I have access to equipment and 3D design programs.