Select two filing cabinets that are both two drawers high. Measure them. Most filing cabinets with two drawers will be around 28 to 29 inches high, which is the perfect height for a desk.
Measure the depth of the filing cabinets. Write it down.
Cut a piece of laminate countertop with a circular saw fitted with a laminate blade -- or have it cut at the home improvement store -- so it is no more than 3 or 4 inches longer than the depth of your filing cabinets and 4 feet wide.
Place your filing cabinets in the area where you want your desk to go. A corner is an ideal place for such a homemade desk as the two walls of a corner area give the desk additional support.
Adjust the filing cabinets so that they are perfectly parallel and that the measurement from the far left edge of the left filing cabinet to the far right edge of the right filing cabinet measures no more than 4 feet.
Place the countertop directly on the cabinets. Adjust it so it's perfectly straight.