Measure the depth, height and width of the dishwasher using a tape measure. Add one inch to each measurement and note the measurements on a piece of paper. Cut two sheets of 1/2-inch plywood to the depth and height of the dishwasher using a circular saw. Cut two sheets to a length equal to the width of the dishwasher and a width of 3 inches.
Cut one sheet of 1/2-inch plywood to the depth and width of the dishwasher. Lay one of the depth-and-height sheets flat on the ground. Screw the 3-inch-wide sheets to the top and bottom of one of the height-length sides using a drill with screwdriver drill bit and four countersunk 3/4-inch screws.
Screw the other depth-and-height-size sheet to the other end of the 3-inch-wide sheets using four countersunk 3/4-inch screws. Stand the cabinet frame up so it is standing on the two depth-and-height pieces and one of the 3-inch-wide pieces. Screw the depth-and-width-size sheet to the top of the frame using four countersunk 3/4-inch screws per side.