>>610401I wouldn't "build one", like from scratch. Not worth the hassle. Buying a used one and setting it up for your application isn't too hard though. Really depends on your fab skills.
I didn't do any structural work on mine (pulled all the plywood off the inside, added insulation, rewired 12v/brakes/lights, added a 120v circuit, added furnace/propane/batt charger) so a buddy and I knocked it out in a summer. We did the same with his trailer a few years earlier, but he did have to reinforce/replace some structure with his (easy enough to do with a 120v mig).
One i'm working on now is a 45ft gooseneck. Bought it as a 3-axle carhauler from a race team in Florida, and it was pretty used. Almost all of the wood was rotted out, cockroach shit all over the polystyrene insulation, some rusted-out spots on the frame... electrical was a mess...
Stripped it down to the steel skeleton. Patched up what needed to be patched up. Flipped the beavertail in the back over so the inside is flat and we've got more ground clearance on the tail end of the trailer.
Pulled the three axles off, installed two 12k axles and reworked the fenders to fit that.
Installed structure for cabinets in the back. Added a 100lb-ish horizontal propane cylinder.
Chassis-saver paint on the skeleton, then install new roof/floor plywood. Working on insulation now, and the aluminum sheet on the roof's in the process of getting glued on (finishing that is this weekend's project).
Then comes electrical, and that's going to be a big project. Sponsors came through and donated a bunch of parts/labor, so with a good size skilled crew we should be able to knock that out in a weekend or two.
Doing screwless aluminum on the side, then the whole thing's getting wrapped (our logo, sponsors, etc. They like that shit.)
Interior... back 2/3, floor's getting rhino-lined. Front living quarters gets industrial vinyl faux-hardwood flooring (the stuff you might find in a restaurant).
