I recently moved across the country and all my stuff didn't fit in the UBox I rented. I ended up shipping about $500 worth of flat rate boxes to get all the rest of my stuff from Oregon to Massachusetts. I Goodwilled a large portion of my furniture and I'm here without shelves for my movies but a bunch of USPS Large Flat Rate Boxes. Here's how I turned these boxes into shelves and what I learned doing it. I'm sure you could use other boxes, but its obviously most uniform if all the boxes are the same size... but maybe you don't want uniform, feel free to be creative.

Step 1: Measure and Cut

I oriented the seam in the box vertical, my reasoning being it would provide more support, but that probably doesn't matter cause then the one on the outside is horizontal.

The box will be sitting on its side when we're done, so pick your orientation. The top flap will be cut at 4 inches from the top (which means you'll be cutting off about 2 inches). Measure and mark a line 4 inches from the top on the top flap and 4 inches from the top on the side flaps. The side flaps are vertical, so we're not cutting these pieces off we're making horizontal cuts to make two flap pieces on the same side. (May need to skip ahead to see what we're doing as I may not be explaining this super clear) I found that if I cut the side flaps about 3 7/8 (almost 4) inches from the top it all lines up a bit better, but I plan to cover mine in white tissue paper so you won't see if they're lined up exactly.

I then found it necessary to cut a small strip off the bottom half of the side flaps and the bottom flap (about 1/4") so that they would fold inward without hitting the bottom of the box.

Step 2: Glue and Fold

Apply glue to the bottom part of the side flaps and the bottom flap. I used Elmers glue on the first sections I made, then when I was running low I added a little flour and water to the little bit I had, then I switched to hot glue when I ran out of that. I think I prefered the hot glue, just cheap low temp stuff.

Then fold those flaps in on themselves. If you fold the bottom flap in last, I found it holds its self all together pretty well. I still held them till the glue tacked up a little though,
I suppose you could just cut these flaps off, but I don't see why not use them for added structural support.

Then glue and fold the top part of the side flaps to the top flap. I thought it looked better to have the top flap on the outside. I used some cheap laundry clips to hold it together once it tacked up a little.

This is just one section of the shelf, I made six sections for mine. Each one will hold 20 DVDs across, but you can also tuck 6 or 7 DVDs on top of them behind the top flap. Great place for movies that you might not want out in the open O_o

Step 3: Final Touches

You can stack them any way you want, but they don't stack well too high. Mine started leaning pretty hard after three high. I hot glued
mine together and then used high strength mounting tape to stick the whole thing to the wall otherwise it would tip over. I think if I reinforced its vertical stance along the sides, maybe 2 or 3 layers of cardboard, while bending it slightly backwards it would stand up better. I thought the easy solution was to tape it to the wall. I tried to hot glue them to the wall, but the hot glue peeled off the paint too easily (and I put a whole glue sticks worth on there). I also tried propping up the front end, but that only helped a little. If you have any other suggestions on making it stand on its own better or better ways to mount it to the walls, share in the comments. Enjoy! :-)