Calculating and Cutting the Truss

• 1). Drive a wood stake into the ground. Measure from it a distance equal to your roof truss and drive a second stake into the ground. Tie a piece of mason's twine tight between the two stakes at ground level. Measure to the center and mark it. Measure up from this point the height of your truss and drive in another stake.
  
  
• 2). Stretch mason's twine from this top stake to the bottom two to create a triangle to the size of the roof truss you need. Stretch a string from the top post to the middle of the bottom string, and tie it off. Use an angle finder with one arm aligned with the angle of one of the diagonal lines of the triangle and the other aligned with this center string. Read the angle from the finder and set your miter saw to that angle.
  
  
• 3). Cut three pieces of two-by-four lumber with their ends mitered at this angle. Cut one to fit the bottom line of your triangle, with one right and one left miter, so that the long points of the miter are as long as the bottom line. Cut two to fit the diagonal lines, minus the 3 1/2-inch height of the bottom board you just cut. Miter each end one right and one left, so that the long points are equal to the diagonal line, minus the height of the bottom board.
  
  

Building the Truss

• 1). Fit these three boards together, so that the two diagonal pieces meet to form a peak. Position the bottom board with its ends up against the lower ends of the diagonal pieces. Measure to the center of the bottom board and mark it on its top edge. Measure from this mark to the bottom of the peak.
  
  
• 2). Cut a piece of two-by-four to that length. Mark the center of one end of this board. Cut the corners of that end on the same angle you used before, so that the cuts meet on the mark you made to create a point. Position this board with its square end on the bottom board and the point against the bottom of the peak.
  
  
• 3). Trace the joints at the peak, both bottom corners and the bottom of the center vertical support onto 1/2-inch-thick plywood squares 12 inches across. Cut the traced joints out with a jigsaw to create plywood gussets. Make two of these for each joint. Apply wood glue and staple these plates to the face of the joint, on both faces of your truss, to join and stiffen the truss. Use an air stapler.