With a larger build like my 5×5, or the 4×4, I would recommend white paint marker.

Put a dot in the center of each shelf, all the way around the unit, at the very outer edges. Then when you have your plywood backing dropped on the back and looking good, it doesn’t matter you are flying 100% blind for the shelves. Why? Because you can make a cheater line out of chalk.

So how do we do that?

You get a chalk line reel from just about any hardware or home goods store. It’s under $10 and is worth every penny for a larger unit, and can be used for plenty of other projects.

This step works best if you’ve already put a couple screws in along one edge. This step might require a buddy. Take one end of the chalk string, and have someone hold it on one of the dots you made. Go across the shelf to the other dot, and pull the chalk line tight. Reach out a ways, grab the line, pull directly outwards away from the plywood, and release. The line will snap back, leaving a nice straight line for you to follow.