If you can afford it go for a full alluminium one, nice and light and no corrosion.
I have a home made bike trailer that a bloke built over 10 years ago and its still going strong. I think most home made jobs tend to be over-engineered and therefore last longer, as opposed to the mass produced that seemed to be knocked together in a hurry.
Check ebay there are always plenty of good trailers (new and used).