Generally, architectural drawings, engineer's surveys, building plans, and similar documents on file with state or local building officials are considered public records.
How do I get blueprints for an existing building?
Contact your local permit agency or records office. Often these agencies store copies of building plans for decades after the structure has been built. Ask what information you need to supply in order to obtain copies of existing blueprints. Provide the required forms and information, and pick up a copy of your plans.