Believe it or not, Huf houses are sort of prefab. On the highest order, though.
I think you can only get them in Europe yet.
I might get one, one day. I'd want to do something about the starkness, though, put in some color. (I'm surprised that I've yet to see a picture of one which is not either black or white.)
See this article and don't miss the videos.
Apparently Huf put up eighty houses between 2004 and 2006... and that's just UK, they supply the whole of Europe!