Build the middle shelf

With a few minor construction changes, the middle shelf can be built to provide various work or display areas. Here are three options: 

Overhang with Drainage   This variation, shown at left, turns the overhang area into a work surface with water drainage. On six-foot-long frames, lay out thirteen 1x4 slats in the center without spaces and then space three slats at each end 1-1/4 to 1-1/2 inches apart. Attach with 6d nails or 2-inch deck screws.

Simple Overhang   In this design, the middle shelf is gap-free and overhangs the potting center legs by about 11 inches at each side. Trim twenty 1x4 slats to 24 inches. Begin assembly by laying two six-foot 2x4 middle shelf frames on edge, spaced to 24 inches. Starting at one end, attach all the slats without spaces with nails or screws. Trim the shelf frames to this length.