everybody and their brother builds trailers here in the midwest region. they are pretty near a dime a dozen. i paid $1100 for a new BP 20ft open with E brakes.
just a few things to look for would be;
dont buy one that the tongue is just welded on about ten inches or so under the front. make sure it extends under the bed at least to the front of the tires if not all the way over them. try to find one that has Chevy or Ford bolt pattern on the hubs. and I would advise getting brakes on at least one axle. another thing to look for, but not so important, is the tail lights mounted flush in the back, those side mounted ones get knocked off or broken all the time. LED's are nice too.
good luck.