Compile a materials list and draw a schematic picture complete with dimensions of the planned 28-by-40-foot barn. Visit the local zoning authority and show them the plan. They will point out any permits required and also help with questions regarding materials and construction methods.
Prepare the ground where the building will be constructed. Clear away debris and level the ground where the 28-by-40-foot building will be constructed with an excavator. To help minimize any drainage problems in the future, slope the ground along each side of the planned barn away.
Position the batter boards and tie the string lines to represent exactly where the sides of the pole barn will be built. A perfect rectangle is required when setting the placement of the string lines. Measure the distance from the front, right corner to the rear, left corner. Measure the distance from the front, left corner to the right, rear corner. These two measurements must be the same. Correct any discrepancies.
Measure along the string line and spray a mark on the ground every 8 feet on the 40-foot length sides of the barn. Measure along the string line and spray a mark on the ground every 7 feet on the 28-foot length sides of the barn. These markings will indicate where the holes must be dug for the poles. Take down the string line from the batter boards.
Use an auger to dig each hole for the poles 5-feet deep and 24-inches in diameter.
Pour an 8-inch concrete footing at the base of each hole. Allow sufficient time for the concrete to dry. Tie the string lines back in place.
Position the poles in each hole. Use a carpenters level to ensure each pole is perfectly level vertically and barely touches the string line. Fill each hole with gravel 3 feet. Check the vertical levelness and the pole proximity to the string line again. Fill the remaining portion of each hole with dirt. Make sure to compact with a rock bar after each additional 6 inches of dirt is distributed. Fasten 2-by-8-inch boards between poles for additional support in preparation for building the top of the barn.
Use a laser level to mark the poles at the front of the building at the desired height for the beams. Use the same process for marking the second, third, and rear set of poles, but measure down 8- , 16- and 24 -inches down from the markings on the front poles, respectively. This will establish the necessary preparation for a linear sloping roof.
Position each beam on top of the poles around the perimeter of the 28-by-40-foot barn. Fasten each beam to each pole with metal plate and galvanized bolts. Use a ships augur to drill pilot holes for each galvanized bolt.
Fasten each truss on top of the beams with metal connector plates and nails. Measure, cut and fasten 2-by-6-inch boards between the trusses to create rafters. Measure, cut and fasten 2-by-6-inch boards between the poles on the two sides and rear side of the barn. The trusses and newly fastened boards will be used to attach the roofing and siding sheet metal.
Secure the sheet metal to the roof and three sides of the 28-by 40-foot barn with washer-head screws. Each screw may need to be gently tapped into place with a hammer before it can be drilled into the metal.