Decide on the dimensions for your workbench top. For example, a 5-foot by 2-foot bench works well for small home improvement projects. Mark the dimensions on the plywood and MDF.
Cut the plywood pieces to match the dimensions with a circular saw. These pieces of plywood will accommodate a 60- by 24-inch workbench top. You need a temporary flat surface to cut the wood. A couple of two-by-fours over two sawhorses will serve well as a temporary surface to cut light- to medium-weight pieces of particleboard.
Set the MDF fiberboard on the temporary work surface. Cut the board to match your marked dimensions with the circular saw.
Squeeze wood glue into a plastic bowl. An empty plastic ice cream container works well. Dip the paintbrush in the glue and brush it on one side of one of the plywood pieces. Press the other piece of plywood firmly onto the glue. Make sure the edges are even.
Place small clamps on the edges of the boards to hold them together while the glue dries. Leave the clamps on overnight.
Remove the clamps from the two pieces of plywood. Spread wood glue over the plywood and set the MDF firmly onto the plywood. Clamp the boards together. Leave the clamps on overnight to let the glue dry.
Screw the drywall screws into the MDF and plywood with the drill to further secure the boards together to make a good workbench top. Use three screws on each end placed evenly apart.