STEP 3:

Nail bottom side rail (F) to plate board (G), forming an upside-down "L" and leaving a 5-inch space at each end. Repeat for other side.

STEP 4:

Flip over the back wall so that top and bottom rails (D) are facing down. Nail top side rail (F) to corner post (A) where top rail (D) intersects. Nail bottom side rail assembly (F) and (G) to corner post (A) where bottom rail (D) intersects.