Hi Bert;

I am glad you said the words "barn" and "popular" because there are so many possible floor plans for buildings. Dave's answer is right on: a side entry or an end entry with three bays.

However, if you start looking at the details and buildings other than barns there are a large number of floor plans depending on the specific use. I highly recomend John Vlach's book BARNS, it has floor plans, elevations and photographs of a large number of different types of barns.

Frame well;
Jim

The closer you look the more you see.
"Heavy timber framing is not a lost art" Fred Hodgson, 1909