There's one here in Austria, too .. Pretty neat to see them at work on it. Won't be finished for 30 years or so, as everything is being done as per medieval techniques, by hand - no tools made anywhere but on-site, etc.
Medieval tech, but with modern health and safety. They arent lifting stones above people on homemade rope. Castle construction was horribly dangerous work by modern standards.
I do question the assertion about tools only being made on site. That doesnt seem very historical. There was plenty of trade in the past. Things like rope and metal were traded far and wide. Making things on site was ussually the cheaper option where possible but, as the OP states, castles were not purely local efforts.
I think you're missing the point about making tools onsite. Surely there aren't many other places from which to get historically accurate tools via trade. If they want it, they probably have to make it themselves.
http://burgbau.at/burgbaufrie/?page_id=428