For this project, I used 6 foot cedar fence posts and 8 foot cedar 2x4s. I used a pencil to space the boards and allow extra air flow. More space between boards is acceptable - even to the extent of dropping off one full board and putting an inch between each side rail.
Another option is to make your sides interlocking layers, one or two boards high - http://cedarstackingcompostbin.blogspot.com/
Since I am composting large amounts of leaves and grass clippings, mine is made in one piece. I don't turn my pile often - when I do, I can either lift the whole thing up or move the pile from side to side. I cut the 2x8x8 posts - cut a 3 foot length off of each end. Save the 2 foot center piece to brace the long sides. Affix your 1/2 (3 foot side) and full fence (6 foot side) boards to the 2x4, leaving the desired gap between each board. Affix each board with 2 weather proof screws - I used coated deck screws.
Attach the vertical posts to the inside of the cedar fence boards, including the short 2 foot boards that are just long enough to brace the long sides. I alternated the dog eared sides, so that each corner had one flat and one notched board.
I used 24 cedar fence posts and 16 feet of cedar 2x4. Note, I was able to do this all along. The trash cans acted as supports - no clamps or saw horses needed.