A well thought out, functional barn should be the center piece of any farming endeavor, horse powered or fossil fueled, that involves livestock. After building and using two previous barns during our lifetimes, I think the one we now have has achieved a level of convenience, efficiency, and economy that is worth passing on.
Good barn doors, ones that will last a lifetime of opening, sliding and swinging in the wind, require careful design and construction. In 1946 the Starline Co., a barn building firm from the midwestern US, compiled a book of barn plans. These two diagrams were in that book and presented excellent information.