My bench-building days are over and I am happy to pass on to you the 'recipe':
You need about 2 metres of treated pine 140 x 35 mm, 10 metres of 90 x35 mm, and 25 metres of 40 x 20 mm; about 78 wood screws 25 mm long (for the 40 x 20 mm) and about 30 wood screws 60 mm long (for all the other fastenings), and six bolts 80 mm long (to join the three pairs of contoured backrest and seat).
Cut the 140 x 35 mm into two lengths of 900 mm each, curved at one end. They are your two armrests, long enough to also hold a beer (or two) ☺
Cut the 90 x 35 mm into three lengths of 700 mm for the backrest and another three lengths of 550 mm for the seat itself. Then use a bandsaw to shape them like this after which you bolt them together:
Cut two pieces of 90 x 35 mm, each 1100 mm long, for the front and back brace (longer if you want a wider bench) and four pieces of 90 x 35 mm, each 750 mm long, for the two back and the two front legs.
Cut 26 pieces of 40 x 20 mm, each 900 mm long (longer if you chose to make a wider bench) to screw across the bench.
For added sturdiness, notch the back brace into the back of the three backrest uprights, and the three seat supports into the front brace.
Assemble like so:
