An advantage of building your own out of an enclosed car hauler or an enclosed utility trailer is that you can build it the way you want it. You can use better materials and better building methods than the cheesy cheap materials and construction methods used on most small trailers. You also don't have to worry about shaking and bouncing it apart when going down rough roads to camp in isolated areas.
If your truck is adequate you can get it there in one piece. I plan on living in mine for the rest of my life once it's built and don't want something that I'm constantly doing maintenance on because it's falling apart. I've got a 28 ft travel trailer and can live in it, but I won't be able to take it where I want to and I don't want to worry about it falling apart on me pulling it down bumpy roads trying to go where I can't get to.
Yeah, it's going to cost me more to build than to buy something ready made, but it will be better and I did mention I'll be living in it the rest of my life.