I added this shelving to my loft/office space in an afternoon. This system is very inexpensive and can easily be setup without many tools or much skill - all you need is boxes and binder clips.

Useful information is included in the photo notes.

Supplies

Boxes: https://www.amazon.com/gp/product/B07JGLHLY4/ref=...

Binder Clips: https://www.amazon.com/gp/product/B06XD3QHLZ/ref=...

Plywood: https://www.homedepot.com/p/Cabinet-Grade-Plywood-...

Screws: https://www.homedepot.com/p/GRK-Fasteners-8-x-2-1-...

Fender Washers: https://www.lowes.com/pd/Hillman-7-Count-3-16-in-x...

OPTIONAL:

Brackets: https://www.ikea.com/us/en/p/ekby-stoedis-bracket...

Plywood: https://www.homedepot.com/p/Cabinet-Grade-Plywood...

I used a scrap piece of plywood.

Step 1: Assemble Boxes

Stack assembled boxes in the pattern you want (I chose a 5x4 grid) and join them together with binder clips. I placed clips at every corner and the center of every vertical and horizontal partition - this really locks everything together and adds a lot of rigidity. I had to push and pull here and there to get all the corners to line up.

Step 2: Base Shelf

This step is optional and allows the shelving to be elevated off the floor.

I used a scrap piece of plywood that is 5' long by about 5" wide - even a 2x4 or 2x6 would work and almost any 3/4" material will work (avoid particle board). One option is to have a piece of plywood cut to size at a home store OR there are many straight edge ripping instructables to DIY:

https://www.instructables.com/id/Cut-Plywood-the-E...

https://www.instructables.com/id/How-to-Break-Down...

Begin by locating studs - I use a rare earth magnet - the magnet is attracted to the screws holding the drywall to the studs.

Next mark a level line at the desired height of the underside of the base shelf - I chose to put my shelf directly on top of an outlet. I have a 6' level but this step can be done with a smaller level and a straight edge, I used the shelf itself. Attach the brackets to the studs exactly at the height of the level line and place the shelf on the brackets. I used the GRK screws from the supplies list at the beginning of this instructable for this step.

Step 3: Attach to Wall

This step is important whether the shelf is elevated or left sitting on the ground - it adds a lot of rigidity and prevents the shelf from tipping over.

Use fender washers or any large washers, it's important have many points of contact and not to compress the cardboard too much. Again, be sure to attach every screw to a stud.

Step 4: Cover Screws

Use the box lids to cover up the screws and give the shelves a more uniform appearance. For these particular boxes I cut the lids down to 12 1/8" x 15" - they're a tight enough to stay in place without any type of fastener or glue.