Build the upper shelves

Upper Shelves  Use two or three slats per shelf for the upper shelves, trimmed to 45-1/2 inches. Trim 1x4 cross braces to match the width of the slats and drive 3d nails or 1-1/4-inch screws through 1x4 slats into the cross braces. These braces secure the shelving to the structure.

Put it all together