With the posts (columns) in place, painted and plumb, you can now measure the distance from each to determine the desired overall length of the lentil. Measure the distance from the outside edge of the columns and add 10" to both ends to create the desired overhang.
Measure and mark the 2 x 10s that will be used for the lentils, and then cut them to length. To create a decorative end-edge for the lentil, use a template and trace along the curve. Cut and sand the edges to create a smooth finish and re-paint the ends. There are several decorative-edge designs that can be used for the lentils. Southern pine experts recommend that you apply a protective finish in order to extend the life of the wood.
Note that the lentils are not light, so you will definitely need some assistance. To assemble the lentils, cut out squares of plywood the same size as the ends of the columns, lay them out and paint them. Measure 10" back from the decorative edges on the lentils and mark each 2 x 10. This allows for the overhang.
Place the plywood squares on the lentils and attach with 3" wood screws. With the double lentil now together, turn it right-side up and set it on top of the front two columns. Once you're sure everything is aligned properly, secure the top of the plywood on the column with galvanized wood screws. You'll have to place the drill between the lentils to do this.
Now you're ready to tackle the back lentils. Lay out the plywood squares and mark where the 2 x 10s attach. Measure from the center column to each end and be sure to add 10" for the overhang. Make the miter cut needed for the alignment over the center column. Assemble the lentils upside down on the ground, repeating the previous steps for the front lentils. Set the lentils in place over the three rear columns, and be sure you have help. Once the lentils are in place, you can attach the plywood along the outside edges of the angled 2 x 10 (Image 1). As before, also add some screws in-between the lentils for extra support (Image 2).