Several books come to mind that might help in your research:
The Pennsylvania Barn by Robert F. Ensminger
Old Barns in the New World/ Richard Babcock
Barns of the Midwest/ Hubert Wilhelm
The Old Barn Book/ Allen Noble
There is also a great deal of historic framing information in the back issues of Timber Framing.
If you are planning to attend the Traditional Timberframe Research and Advisory Group annual symposium March 12-14, you will meet more than a few framers with experience in the type of roof system you are studying.
This forum probably will supercede the members section BB. Thanx for using it.