Also have a look at the beams themselves. Hand hewn usually indicates an older structure. Sawn beams with vertical saw marks a little newer, sawn beams with circular saw maks after ca. 1850. Even after people started sawing their timbers some of the really long ones may be hewn (due to saw mill constraints) or have been salvaged from an earlier structure.

If it is scribe rule frame you may also find the master compass settings (circles) scribed into one of the beams. These were used to refernce the compass settings throughout the buildings construction.