I would check a local trailer dealer to see how much you could get one for. A lot of times they may even have a used one that they took in on a trade. I wouldn't buy one of those little ones you are just wasting your money and taking a chance on loosing your quad. you really need to take into consideration how much weight you're going to be hauling. Most utility ATV's are around the 580 mark dry weight. add 4 gallons of gas at 5lbs per gallon. Plus another 5 to 10 gallons in a can. a quart of oil at 7lbs per gallon. Plus any gear or accessaries you carry on the quad.

Most of these little trailers just aren't made to handle that kind of weight. When looking at the trailer you need to get the load ratings for the tires, axles, springs, and hubs. If you exceed the weight in any of these areas then you are asking for trouble.
For me I'm not trusting my $6,000 dollar quad to some $100 dollar trailer. Even if I have insurance.
If you find a homemade trailer just make sure what the load ratings are on the items I mentioned above.
There is nothing wrong with a homemade trailer if it is done right. My dad is a fabricator and is building me an 8X14 four place ATV trailer. But he knows how to build them and is building so that it will handle four utility quads easy!!!
Good Luck!!!
Take your time and do it right!!!!