Cut out a 2.5-inch diameter hole in the right hand, rear corner of the 90-inch by 70-inch panel, 2-inches in from the edge. Use the hole saw and wear safety glasses while cutting. Cables for the computer and screen will be fed through this opening.
Place the 90-inch by 70-inch top panel, flat on a clean and smooth work bench.
Run a continuous line of wood glue along the 26.5-inch long, top-surface edge of the first 70-inch by 26.5-inch side panel. Place this panel against the right-hand side surfaces of the top panel, standing vertically.
Run a continuous line of wood glue along the 26.5-inch long, top-surface edge of the second 70-inch by 26.5-inch side panel. Place this panel against the left-hand side surfaces of the top panel, standing vertically.
Leave to cure for an hour and then nail, using the finish nail gun, both side panels in place. Place the nails exactly along the lines where the glued was applied.
Position the 90-inch by 26.5-inch back panel vertically on the top-surface edge of the top panel. Request the help of an assistant to hold the back panel in place.
Position the left side of the back panel next to the side surfaces of the left-hand side panel. Nail the back panel to the left-hand side panel.
Position the right side of the back panel next to the side surface of the right-hand side panel. Nail the back panel to the right-hand side panel.
Request assistance from your assistant and turn the computer desk right side up. Nail the top panel along the length of the back panel.
Leave the computer desk to cure for a day.
Stain the computer desk to match existing furniture.