I didn't say people would build their own roads. I said people would pay private road contractors directly instead of through a governmental middle man. When connecting city to city, so long as there is market demand for those roads then the private road companies will build the road so long as they can make a profit and there are several ways by which they can do this. Sure I guess they could start a go fund me type thing, but I think it would be far more likely that they'd use some form of toll system to pay for it and maintain it.