Looking back now I feel I was very ignorant of how old barns were built, but reading Radojkovic's book 'Barn's of the Queen's Bush', I realized that the most important part of the barn construction was the part you can't see. These are the hidden mortise and tenon joints, and the pegs that hold them in place - all hidden from view except for the ends of some pegs.
The work of a barn-raising is to raise the bents to stand upright, and then to manhandle the purlins and girts into place to hold them together, pegging the joints are they are fitted. The mortise and tenon joints and the pegs are the magic that keeps it all together. After the big event the farmer, relatives and friends would finish all the roof and sides of the barn in the coming weeks.
I did see a barn- raising once, as a young child, when two barns were destroyed by a tornado. We drove by a few weeks later and a huge crew of men was rebuilding both barns! This photo is from the cover of 'Barns of the Queen's Bush', with full credit for what I've learned to Jon Radojkovic.