Legal Question in Business Law in California

Without more particulars, I'd think that the builder would probably be adequately protected in its limited role as a "design builder" by a contract fully expressing the intentions of the parties. This would be in addition to terms relating to engineering/mechanical aspects, payment terms, and the usual contract boilerplate in a contract for the construction of something routine. Since the details of what's to be built may be relatively vague, the contract should give the builder more latitude than usual as to its responsibilities for the performance, appearance, suitability, etc. of the end result. Finally, I don't believe "steps taken to create the concept design" would fall within the boundaries of what is subject to trademark or copyright. At most, production steps might be patentable.

Actually you can "copyright the steps taken to create the concept design."

Engineering, technical and scientific drawings are protected by copyright. If you're hired as an employee the drawings become a "work for hire" and belong to the employer. But if you're just a consultant the drawings you create belong to you and you can license them to the purchaser. If you're a consultant the finished product itself belongs to them since that is what they buy, but not how you came up with building it.

If you want a licensing agreement drafted I can help.