Over by the big barn you will see a partially grenaded house that is still smouldering.
Go inside and head to the second floor.
Now looking at the haybarn, turn back toward the broken outer wall and jump.
You should find that you can jump higher and higher until you are in the rafters
Go prone and you can spew out of all walls and still fire.
Great for sniping, rocket launching those pesky tanks and GPMG set-ups