I agree with Brad...this is an old one...as threads go...

Further, in concurrence with the comparison of "stick building" the entire general modalities of timber framing an "eyebrow" is more what you would find in shipbuilding or fine furniture making, even if the 50% or more of it is hidden...It's a different world to "general contracting."

I would also add, that much of it can and is done without a lot contractor type "measuring" (per se) as it would follow one of the lofting, templating, and/or "story poling" methods, reflecting levels of accuracy that you just do not find on most "modern buildings" built today in domestic architecture...