I honestly believe, having built a utility trailer, that you would be better buying instead of building. There are some significant unknowns that you may run into and much comes back to how the trailer will handle behind the bike, and solving the inevitable hitch issues.
BoB has been making trailers a long time now, and whatever problems (except for their rather limited stated maximum speed downhill) have been ironed out. I have never heard on any of the forums of the basic BoB failing except for some wheel issues. The integrity of the construction cannot, I think, be disputed.
The Burley-type trailers are another option, and while the extra wheel and width might become a liability along roads that have, for example, rumble strips, or narrow shoulders, there have been a few people who toured with them.
The resale value is another consideration. There are some "homebuilt" trailers that come up from time to time on eBay in Australia, and they are almost unsellable. No-one ever has a problem selling a well-used BoB, and only slighly more problems selling Burley-type trailers.
site will likely turn up people who have toured with both, and maybe have built their own.
As a note, I am someone who prefers panniers to trailers.