I've found dating New England buildings is easier and more effective if you focus on exterior architectural details rather than joinery or hewn/sawn timbers, etc.

Georgian, Greek Revival and Victorian eras are displayed in roof elements and cornices, even on barns. I then look at interior details to support what I see on the outside. The whole thing begins to speak... This is a strategy I've come to over my surveys and have found it pretty accurate here in Maine.

When I speak of roof pitch as an age indicator, it's a generalization; I'm referring to pitches of 8/12 and under as a kind of demarcation, not "odd pitch." But odd pitch is certainly an interesting element to explore.

I think another thread here somewhere (god knows where) discussed 8/12 or 1/3 pitch as a very common pitch in the early 19th century: it could be walked, yet still shed water/snow fairly well. Perhaps roof staging/brackets were something they tried to avoid in the old days (at least on barns)??

Of course, a lesser pitch required less $ and material, too.