Measure and mark the outline of the area that will be covered by the overhang.
Connect three boards with screws to frame the overhang outline. Attach to an exterior wall of the pole barn with screws to complete the outline framing.
Dig post holes at the frame corners opposite the pole barn wall with an auger. Holes should be at least five feet deep. Insert a 4-by-4-inch post in both holes and fill with concrete mix. Fill the frame with concrete for a level surface under the overhang.
Measure the distance from the edge of the pole barn roof to the far edge of the 4-by-4 post. Add 18 inches to the measurement and cut a 2-by-10-inch beam to that length.
Place a 2-by-4 board across the 4-by-4 beams to connect the overhang posts. Count the number of pole barn roof trusses between the edges of the overhang outline and cut enough 2-by-10 inch boards to the length determined in the previous step to attach to each truss.
Remove the fascia from the pole barn roof trusses, if present. Attach each board cut in the previous step to a roof truss with a rafter tie and nails or screws.
Cover the exposed end of each 2-by-10 inch beam with fascia board.
Attach tin roofing sheet to each 2-by-10-inch beam with roofing nails to cover the area beneath the overhang.