Dimensions: 10ft x 6ft x 28 in deep. 12 inches high from ground to seat height (4-inch high legs +4-inch large pallet thickness x 2). Backrest 20 inches high and follows length of the seating. I was able to find four large 8ft x 4ft pallets on Craigslist at a warehouse.
I cut two of them in half to one side of the center beam. It is made one-half slightly wider than the other. The larger half was used for the seat. The narrower sections were used for the back supports. To me the seats more comfortable, I added more slats to fill in the gaps. Sometimes it required prying up slats and then screwing them back down. I used 1 1/2 inch decking screws instead of nails. For boards that were cracked or brittle, I preferred drilled to prevent further splitting if wood.
Pallets were screwed on top of each other by driving decking screws at a slight angle at the edge of a brace and a slat from the bottom pallet up onto the top pallet's brace. It made it almost impossible to see the screws but also made the pallets very sturdy.
The slats left from cutting pallets lengthwise were used as uprights for the backrest. I cut out a notch that allows them to mount on the top surface and back surfaces perpendicular to the seat. These were pre-drilled and screwed down with the decking screws. I also glued the mating surfaces with tight bond wood glue before screwing them in place. A primary pallet brace support was then placed across the top of the uprights and glued and screwed into place. As the sectional is an "L" shape, I put a backrest across three feet lengths of the end section. This left another three feet open w/o a backrest. Using leftover slats and a few other pallet pieces, I filled in the spaces between back support uprights. These were screwed on-center of uprights.
The only area left to fill in with slats was the corner between the two backrests. The required cutting slats at compound angles that took a lot of time and trouble. I made the feet from 4×4's cut to 4-inch lengths. His bevel was created by measuring in from 2 1/2 inches from each side and drawing a line. This made a small square centered on the bottom of the block. I measured on each side 3 inches and drew a line around the perimeter of the base. I then joined the lower line up to the 3-inch line, and this gave me my angle. I set my table saw for this and cut it out. As my saw didn't cut all the way through I had to flip the piece to complete the cuts on all four sides. I made eight legs for the long section and 6 for the shorter section.
The legs were screwed to the bottom slats of the bottom pallets by driving decking screws through the pallet slats into the top of the legs. I also glued the two surfaces before screwing them in place. As I wanted a rustic look, I did not plan or sand any surfaces. I did paint it with a graphite gray outdoor paint. The cushions we found on sale at Ikea. We got real lucky there. Regular price was $25 for the white seat cushions. We paid about $7 as they were on clearance. The back cushions were the same story. Otherwise, the cushions would be the most expensive part.