Place the cabinet Base Plate on the sawhorses. Using the Base Plate as a work platform, nail the front and rear corner Vertical Supports to the End Panels, making sure they are both flush and square. Measure and mark the positions of the End Panel Assemblies on the Base Plate. Stand the End Panel assemblies on the Base Plate in their final locations. Install the Bottom and Top Rear Horizontal Supports to the inside of the End Panel assemblies with wood screws, making sure that they are flush and square.
Measure, mark and place the above assembly on its proper location on the Bottom Plate. Using the finishing nails, toe nail the assembly in place, leaving about 1/4" of the nails exposed.
Attach the Top Rear Horizontal Support to the end assemblies with wood screws. Toe nail the Front Center Vertical Support in place. Do not drive the nails in all the way at this time. Leave about 1/4" of the nail out of the wood. This will allow for easier removal at a later time if the piece of wood is not in the exact right place.
Drill the pilot and countersink screw holes in the end plates and bottom horizontal supports. See the photo below for an illustration of how this will look. Attach the assembly to the Bottom Plate with the 1 1/4" flat head wood screws.