You may find these other links helpful in gathering infomation about architectural styles and forms in Pennsylvania and the United States.  

http://crgis.state.pa.us  This searchable website permits viewing of all of Pennsylvania's identified historic resources  including those listed or eligible for the National Register of Historic Places  or found through historic site surveys.  The CRGIS is being updated constantly to record new information about hiistoric buildings and districts, as well as archaeological sites.  A wide variety of search queries are possible.  Full National Register nomination forms are included for those properties that have been listed.   An assigned password is required for access to archaeological data, but the public can view all historic property information by using the public login. 

www.cityoflancasterpa.com  This city website provides an illustrated guide to architectural styles in Lancaster, Pennsylvania.

www.cttrust.org/index.cgi/7388  This website of the Connecticut Trust for Historic Preservation provides an architectural style guilde as well as rehabiliation, preservation, and real estate tips for historic properties.

www.explorepahistory.com  This educational history-based website provides information for research and tourism in Pennsylvania, including a guide to all historic markers and background information on important historic themes.

www.greatbuldings.com  This website features over 1000 photos of buildings of all architectural styles from all over the world and includes a searchable database.

www.westwinddesign.com/glossdes.htm  This website offers a glosary of historic architectural terms and a guide to select historic styles.

http://preserve.bfn.org/bam/vocab/vocab.html  This website offers an illustrated dictionary of architectural terms useful in describing historic buildings.

http://jan.ucc.nau.edu/~twp/architecture  This website on the Architectural Styles of America was created by Dr. Tom Paradis, a professor at Northern Arizona University features photographs and a style guide.

http://www.loc.gov/rr/program/bib/newdeal/habs.html  This website offers a collection of  the HABS/HAER drawings and photos collected from the 1933 to the present with images and historic background.

http://www.nps.gov/history/hps/tps  This is the website of the National Park Service and contains a great variety of preservation related information.  This particular page directs you to the Historic Preservation Services Division, Technical Preservation Services.  TPS is responsible for the publication of numerous briefs on the proper care and repair of a wide assortment of historic building types and materials with associated background provided. 

http://nps.gov/history/nr/research/index.htm  This NPS website page provides information about the National Register of Historic Places and includes a NRIS searchable database of listed historic properties accross the country.