I followed the plan but made the sofa longer, the cushions were on clearance from Pottery Barn for $160 and the cushions are about 96 inches wide.
I used weather treated wood and did not want to spend more since its my first project. I used Behr exterior weatherproof transparent stain. I attached the seats back piece using a 2x2 attached on the bottom with screws and pocket hole screws are used to attach the 2x2 to both sides of the arm frame.
I love how it turned out. I was not expecting for it to come out this nice but I am really impressed.
I hope you guys like it too!
Total cost is around $240 including paint, wood, screws and the cushions.