Step 6: Lay Out The Ceiling Cleat
Use a 48 In. level to make a plumb mark on the ceiling above each end of the ledger. Use a framing square to make a line on the ceiling square to each end. Then use a chalkline to extend these lines 48-1/8 in. from each end. (That extra 1/8in. will make it easier to slide the plywood floor into place.) Snap a line parallel to the wall between the ends of the two lines. Use a stud finder to mark where the line crosses joists in the ceiling.
This project assumes that the ceiling joists in your garage run perpendicular to the ceiling cleat. If the joists run parallel to the cleat, you have two choices: You can adjust the width of the storage unit to the nearest joist. Or you can make five 2x4 cross-cleats to span two joists. Use 3-in. lag screws to attach the cross-cleats through the ceiling into the joists. Then lag-screw the ceiling cleat to the cross-cleats.