I prefer the stock bike approach however, if you can converse directly with the builder on fit and specifics then this is an excellent approach also. The direct dialogue better ensures the builder understands how you ride and, what you desire in a bike.

However, I get nervous when another interpreter is put between myself and the builder. Not that this means you don't end up with what you want but, there is more risk involved in this approach and I prefer to avoid it. If there is a money back guarantee then this approach would be acceptable.