Adam,
Might want to check out the Library of Congress website. They have architectural records including recent architectural surveys of historic structures. These include elevations, plans, and sometimes landscape surveys and site plans.
http://memory.loc.gov/ammem/collections/habs_haer/
You can search as well as browse by subject.
http://memory.loc.gov/ammem/collections/habs_haer/subject.html
Or by place.
http://memory.loc.gov/ammem/collections/habs_haer/place.html
Some of this is almost priceless. They include large format tiff images many with dimensions or graphic scales. Some also include details and sections.