This is A great book which offers over 400 pages of information, with almost 1,000 illustrations , photographs, plans and elevations, to illustrate the different barns, uses, history and regional influences.
“While there is much that can be learned by browsing through these assembled images, the photographs and drawings in Barns are arranged in order to convey a particular story of movement across time and space. Barns serve here as physical evidence of the key stages in American settlement history and as markers of specific pathways followed during the process of transcontinental migration. The flow of images runs from the eighteenth century to the twentieth and from the East to the West.”
http://www.loc.gov/locvideo/barns/