Clarification regarding patent and copyrights

We are manufacturing an electronic product for a client of ours. The client has a utility patent for the product (idea). But we have developed the product in flesh from its circuitry to its 3D modelling, schematics etc. The client has not contributed financially to the company in the product development whatsoever. Now since that we are moving from sampling to manufacturing stage we are drafting a new contract. In the contract we claim to have the rights to all the circuit and CAD designs since we developed them. We also acknowledge that the client is the sole owner of the idea and without his permission we cannot manufacture or sell the product. The client has only paid for the samples and we did not charge him anything for product development and are providing the solutions for free. But that doesn't mean he owns the copyrights. He wanted us to contact an attorney to shed some light on this topic.