How should I deal with "ownership of documents"?

Always remember that drawings, specifications, reports and other documents that are produced by you are instruments or deliverables of your professional services and are not products! Also, you are the ultimate owner of these documents and any reuse by your client will only be done for additional compensation. Building codes vary from location to location and the exact duplication of an approved design in one location can be in violation of building codes in another. You should include a "hold harmless, indemnity and defense clause" for unauthorized reuse in your contracts for professional services.