I bought treated lumber, including 4-4"x4"x8' posts and 2"x4"x8' and 2"x4"x10' boards, to start the project. I dug 4 holes with shovel and posthole digger in a 4'x5' rectangle where the old bench had been, moving some of the flagstones I had put around the locust tree that had been there. I mis-measured and had to fill in and re-dig one hole and widen a couple of others to get a square layout for the posts. I started with the 2 along the W edge, using scrap wood for braces to ensure the posts were plumb and clamps to hold the horizontal piece in place while attaching it to the posts. I used a level to ensure the posts were plumb and the horizontal piece was level between the 2 posts, rather than measuring up from the sloping ground.