Place masking tape on the garage floor where you want to install the cabinets and park the largest car you own in the garage. Open and close the car door to see if there's room for the cabinet in the location you chose.
Use a stud finder to locate the studs in the wall where you are building the cabinet, if the wall is finished.
Cut two end panels out of 1/2-inch plywood that measure 4 feet long and 2 feet wide, and three divider panels that measure 4 feet long by 22 1/2 inches wide.
Place one of the end panels against the ceiling and the back wall of the garage. Screw the end panel to the stud every 12 inches with 2 1/2-inch screws.
Cut pieces of 2-by-2 board that are three inches shorter than the end panels. These will be the wall cleats that are used to attach the cabinet to the wall.
Hold the cleat for the second end panel over the last stud where the cabinet is being installed, positioning it so that it's 1 1/2 inches beneath the ceiling. Nail the cleat to the stud through the wall.
Hold the second edge panel against the outer edge of the cleat, placing the top edge against the ceiling, and screw it into the cleat with 2-inch screws.
Cut the lumber for the two ladder rails of the cabinet by cutting four 2-by-2 boards that measure the length of the inner edges of the end panels, and 20-inch long 2-by-2 boards to be the rungs of the ladder rails. You need two rungs for each stud behind the cabinet.
Assemble the ladders by nailing a rung to the end of two parallel ladder rails, which will form a rectangular frame. Nail more rungs into the middle of the ladder, spacing them to match the location of the studs in the wall.
Attach cleats to the inside edges of the end panels 1 3/4 inches below the ceiling. These cleats are temporary, and will be used to hold the top ladder in place as you install it.
Slide the top ladder into position on top of the cleats. Attach the ladder by screwing one of the end rungs into the end panel, each of the center rungs into the ceiling, and the second end rung into the other end panel. Remove the temporary cleats.
Snap a chalk line 1 1/2 inches beneath the bottom of the end panels by driving a nail partway into the wall near the end panel and running it across the wall to the other end panel.
Attach temporary cleats beneath the end panels, and slide the second ladder against the wall on top of the cleats. Screw the end rung into the first end panel, and nail the ladder rail to the wall behind the shelf unit. Screw the second end rung to the other end panel, then remove the cleats.
Nail the divider wall cleats to the back of the wall over the studs, then drill evenly spaced 3/16-inch pilot holes through the cleats and into the studs. Screw the cleats to the studs with 3 1/2-inch lag screws.
Cut 1 1/2-inch square notches in each corner of the divider panels. Attach them to the wall cleats and ladder rungs with 2-inch screws.
Cut the tracks for the sliding door rails with a hacksaw to fit between the end panels. Place glue on the bottom of the top rail, tack the top track to the rail with one-inch brads and then attach the bottom track to the top of the bottom rail with one-inch brads.
Screw a 20-inch long cleat made of 1-by-2 board to the bottom of each divider panel.
Take the measurements for the cabinet doors. Determine the width by dividing the length of the door tracks by four -- because there will be four doors -- and adding 1/2-inch to the width of each door so that they overlap. Determine the height of the doors by subtracting 1/8-inch from the measurement between the inner edges of the door tracks.
Cut four doors out of 1/4-inch plywood that fit the dimensions. Place them in the tracks to ensure that they slide in the tracks. Remove the doors.
Drill 3/4-inch holes into the doors for the knobs -- called finger pulls. Glue the finger pulls into the holes.
Screw the 1-by-2 cleats to the end panels and divider panels at the heights you want the shelves to be. Cut the shelves to fit the dimensions inside the cabinet out of 3/4-inch plywood.
Nail trim panels to fit the front edge of the cabinet.
Paint or stain the cabinet.