Honestly, I'd get one of the Downtube $600-$700 IGH bikes, either the 16" or 20" wheeled version. With the belt drive which comes standard on either of them, you would not be able to build yourself a similar bike for less. I get bike shop discounts on parts. I know how to build my own wheels. And I would still go with a stock Downtube before I tried putting something together on my own, as proposed in the original post.