Draw a simple sketch of the desk on graph paper. The desk should be at least 24 inches wide. Write down the dimensions of the top. Take these dimensions with you to the hardware store.
Purchase a piece of sheet lumber or sanded plywood that is trimmed to your dimensions.
Smooth the rough edges of the wood with fine grit sandpaper. Work your way around all four sides of the desktop to create a smooth finish. Stain or paint the desktop.
Set the filing cabinets in place where the desk will be constructed. Apply construction adhesive to the top of the filing cabinets.
Place the lumber over the two filing cabinets to create the desk. Press the wood firmly into the adhesive. Open the top drawer of each filing cabinet. Clamp the lumber to the cabinet with a clamp. Let the adhesive dry overnight.