Place the 25 inch-by-48 inch section of oak on a flat surface. Apply wood glue to the top edge of the two oak balusters, and press one in each corner along one 25-inch edge of the oak section.
Place the L-brackets along the top of the baluster where it is connected to the 25 inch-by-48 inch section of oak. The L-bracket should be placed along the side of the baluster which faces the opposite baluster. Drive one 3/4-inch screw through each hole in the L-bracket to join the wood together permanently. Generally, there will be one hole on the top of the L-bracket that connects to the baluster and one additional hole resting along the back of the 25-by-48 inch section of oak.
Place the 25 inch-by-11 inch section of oak on a flat surface. Apply wood glue to both 25-inch edges and press one 29 inch-by-25 inch section of oak onto each side. Hold in place for 1 to 2 minutes. This will create a U-shaped structure. Drive one 3-inch wood screw every 5 inches along the length of each side to join the three sections of oak together permanently. This will take a total of 10 screws to complete.
Flip the assembly of oak you created in step one over and rest the end opposite the balusters over the U-shaped structure. Drive one 3-inch screw every 12 inches along the length of both sections of oak the flat top is resting upon. To complete this, you will use a total of 6 screws.
Measure 15 inches along each 25 inch-by-29 inch section of oak. Mark the 15 inch locations on the inside of the U-shaped structure. Apply wood glue to the 25-inch edges of the remaining 25 inch-by-1 inch section of oak. Insert the wood section into the U-shape structure and line up the glued edges with the two 15-inch marks. Drive one 3-inch screw every 5 inches along the length of each side to create a permanent shelf in the desk. This step will take a total of 10 screws to complete.