You can build your own travel trailer by following plans that can be obtained from a specialty company, such as Glen-L RV Plans, or by starting with a small flat-bed trailer and doing the design work yourself. Either way, you need shop space and a good selection of tools.
Building from commercially available plans offers a few advantages. One is that the designs are tried and proven, and the plans come with materials lists and basic instructions. Another advantage of a plan kit is that a good one includes full-size layout patterns that simplify many aspects of the job, such as placing window and door openings, wheel-well cut-outs and plumbing and electrical drop-outs.
Getting a small flat-bed trailer and building your own creation lets the money that would have been spent on plans go into your trailer, and it also gives you a lot of satisfaction when the finished product rolls into the campground for the first time. However, a scratch-built trailer most likely need to be small and little more than a basic sleeping area. In contrast, plans are available that guide you in building a full-size 20-foot trailer with kitchen, bathroom, and all the amenities.
One thing to remember for both types of builds: everything must be done with care and quality to ensure safety when towing the trailer down the road.