After the barn is stripped of all boards. Study the frame. You need to stand in the shoes of the framer who put it up, and take it apart the exact opposite way he put it together. You'll need a full set of drawings including all dimensions so you can label the drawings and then the parts so you'll know which one goes where, once disassembled.
Everything will need to be properly braced off so that it can come apart safely and without any damage.
You may need a man lift and a crane to do it.
