Unless a term is defined in the law, it is given its dictionary and/or common definition, not one related to local codes or real estate terms. To do otherwise would make the law change from city-to-city within a state: A no-no.
A bedroom is not a structure, the building (house) is the structure a bedroom is a part of the structure. From http://www.legal-explanations.com/definitions/structure.htm A structure is defined as the physical development made in a land with a purpose to provide accommodation . For a construction or development to be a structure it must have an enclosure and a roof with provisions for entering within it. A structure is the first stage of construction of any building.
From http://legal-dictionary.thefreedictionary.com/structure anything built on land from a shed to a highrise.