The little one was actually a post-it note sized piece of paper from my computer desk. The larger one was a piece of scrapbooking paper. As for finished size: The small box started as a 3x3" piece of paper and ended up as a 1" square box. The larger one started as a 10x10" piece of paper and the box size is approximately 3.5" square.
My mind is spinning with ideas for these neat boxes; they could be used to keep all kinds of things in them!
Here's the pin where I got the idea, along with something really cool to do with them - boxes inside a box! I can think of a lot of neat ideas for this in the way of crafty storage.
Also, I saw some pins where people made covered gift boxes this way. I'm assuming you'd make the top just a bit bigger, so that it would fit over the bottom box as a lid. That is definitely a neat, crafty way to give gifts.