Awesome sight, tons of people willing to help. Seems to me that if you already have some of the parts, a small engine, metal, a welder to fabricate it or a hookup with someone who can, that building your own can be fun, educational and come out to be specific to what you want.
However it also seems like theres a lot to go wrong, and you may have to trouble shoot some stuff. WIth the prices on used nice conditioned ones what they are, I would probably purchase one to start off, perhaps starting a project to build my own for the "neatness" or whatever.
Best of luck!