Lay an 18-inch plank of 2-by-12 lumber flat on the work surface. This is the central pedestal for the bench leg.
Place a 12-inch piece of 2-by-2 lumber across the 12-inch face of the leg, flush at the corners of one end of the leg. This is the brace plank. Place a 12-inch piece of 2-by-3 lumber across the face of the leg, flush with the corners of the other end for the foot of the bench leg. The 3-inch side of the 1-foot plank should be lying against the leg.
Drill four evenly spaced pilot holes through the brace and foot planks into the leg. The pilot holes should be sized to fit the shank of 3-inch wood screws.
Fasten the foot and brace planks to the leg plank with the 3-inch wood screws through the pilot holes.
Turn the leg over, so that the side without a brace plank or foot plank is facing up. Attach another brace and foot plank to this side as you did the first side. Repeat for as many legs as you need, with one leg for every 2 feet of bench top.