Step 1 Measure and cut sleepers to length. Cut two 200 x 1600mm seat lengths, six 200 x 400mm leg pieces and four 400 x 100mm cleats. Plane along all edges to clean up and sand all surfaces smooth.
Step 2 Butt join 1 seat length to 1 leg piece. Drill a clearance hole through seat and a pilot hole into leg, then screw together. Repeat in centre of seat length and also at opposite end. Repeat for remaining seat length and leg pieces.
Step 3 Turn seats upside down and push together so edges are flush. Put 1 cleat in angle between seat lengths and leg pieces at 1 end and secure into legs with screws. Repeat for opposite end.
Step 4 Position cleats on both sides of centre legs and secure with screws. Turn seat over, then screw through top of seat into cleats. Paint seat with at least 2 coats, allowing to dry between coats.