Hi DJ,
I'm not a timber framer, but have an architecture degree and an interest in traditional building methods. I would suggest:
1. "Learn to Timber Frame: Craftsmanship Simplicity Timeless Beauty" by Will Beemer
He describes some common layout systems for cutting the joinery, tools needed, very basic engineering, etc. and includes a basic 12'x16' building.
2. Elliot & Wallace's "The Timber Framing Book" which I find to be a good practical reference.
3. Basic Design Issues in Timber Frame Engineering" and the second part "Basic Design Issues in Timber Frame Engineering II" from tfguild.com. Lots of good TF engineering info at tfguild.
4. I also like the 6 articles from www.ncptt.nps.gov that describe "Historic American Joinery" The first is called "Historic American Timber Joinery, A Graphic Guide: I. Tying Joints: Tie Below Plate"
Just an FYI, there is a span calculator at AWC.org or you can look things up in their published tables.
Personally, if I were to design a Timber Frame, I would calculate the spans and loads myself then take it to a structural engineer to double check.
cheers,
Sidney
