In the anime Tom is the best shipwright there is, but how did he get the blue prints to the Pluton. Did he write them himself, and if so how did he get the information needed to do so?
While Pluton has yet to appear in the story proper, it has been referred to as an ancient ship capable of massive damage and destruction. It was built on the island of Water 7 sometime during the Void Century, and the shipwrights kept the blueprints as a safety measure, in the event that Pluton fell into the wrong hands; fortunately, the ship was lost to history before that could happen. The blueprints were passed down through the generations, and ten years prior to the main storyline were held by the Fishman carpenter, Tom, of Tom's Workers.
Therefore the blueprints were created during the Void century about 800 to 900 years ago and passed down through generations. Tom was the best shipwright of his generation, but when he was younger, there was probably another shipwright as good or maybe even better than Tom, from whom Tom had inherit the blueprints from. The blueprints, could be a real danger for society and should have been destroyed earlier, but as Tom mentioned, it is not the ship that does the wrongdoing, it's its captain. Shipwrights just build the ship. So they kept the blueprints around, to be able to defend themselves, if the original ship ever fell into the wrong hands or to defend themselves against any of the other ancient weapons. In Enies Lobby, Franky destroyed the blueprints, although it is not clear whether he had made a copy or whether he had memorized the blueprints. He is a robot after all. So it might still not be the end of Pluton as we speak.