Cut the 96-inch timber into four equal 24-inch lengths using a miter saw. These will be the supports for your bench, positioned horizontally to hold the seat portion of your bench.
Drill two 3/8-inch holes that are 4 inches deep into the 24-by-6 inch surface of two of the 24-inch timbers. Place a timber with the holes in it on top of another 24-inch timber that does not have the holes in it. All four vertical sides of these two timbers should be flush. Screw the timbers together by screwing through the 3/8-inch holes and into the timber that is beneath it. Repeat this process with the other two 24-inch timbers.
Space both sets of 24-inch timbers so they are parallel, standing on their 6-by-24 inch sides, so they are 48 inches apart. Set the 72-inch timbers on top of the 24-inch timbers so they are perpendicular to the 24-inch timbers, and so there is a 6-inch overhang at both ends. Screw the 72-inch timbers to the 24-inch timbers using four screws for each timber. Drill a 3/8-inch hole that is 4-inches deep for each screw.