I've been thinking about building one for some time now and if I do one requirement will be some kind of brake system. A friend of mine almost became a PETA poster boy when he jackknifed going down a hill and caught an antler in the back. The connection used by BOB trailers is hard to beat.
http://www.bobgear.com/bike-trailers/trailer-forks. Other trailers that attach to the seatpost can cause a squirelly ride when you have alot of weight behind you.
