Besides being fantastically alliterative and tough to say ten times fast, the title, Bert Breen's Barn, is pretty straightforward. This guy named Bert Breen once built a really sturdy barn. Our main character, Tom, gets it into his head that he'd like to move the barn to his place and make a better life for his family. And there you go.
The barn acts as Tom's primary motivation and as the central symbol throughout the novel (jump over to our "Symbolism, Imagery, Allegory" section for more on that), so why not name the book after it as well? Done and done.