There are many storage unit available to store your 12 x 12" papers and they all cost money! Some of them are very expensive. Here is a fairly inexpensive ways to set up your own paper storage system. I bought this rolling file cart at a local, chain office supply store. It did not come with the file folders. When I bought it the retail price was around $50 but I got it on sale for about $30. I would suggest that you watch for sales for something along this line. It has bars that are adjustable to file any size that you want. The section with the olive green files is for my 12 x 12" papers. The section going the other direction is for my 8 1/2 x 11" papers, mainly cardstock.
Folders to store 12 x 12" papers can be rather pricey so I made my own. I bought a box of legal size file folders. These were 15" x about 9 1/2." I also bought a roll of packing tape or clear 2" wide tape. I cut the bottom of each folder down the seam/fold which gave me 2 pieces.
I used old folders that I had on hand to make the larger section or you can buy additional smaller folders or use any heavy paper you have on hand, such as construction paper, old cardstock, etc. I used the old folders the width of the folder (11 1/2") and cut them above the fold about 5" on each side of the fold.
Measure exactly where the folder will fit on the cut larger folder to make it hold the 12" paper. Then place the smaller cut folder on each piece of the larger cut folder. Tape together with the 2" tape so that about 1" of the tape fits on each folder. Do that on each side. Your folder should now hold your 12 x 12" papers without any trouble. You can hang them in any type of hanging file that will accomadate this size. If you don't like or can't find the rolling cart, you should be able to find other types of carts, crates, or cabinets that will hold legal size hanging folders. Any of these will work for you larger patterend papers.
I hope that this is a little bit clearer than mud (lol) and that you can understand how to make these larger folders. It's great to have the paper hanging like this. I have found that with using standing paper storage units, my paper sags and bends. Using the hanging file folders keeps my paper straight, as good as if it were laying flat but much easier to find what I want. I use the little stick up tabs to organize my papers with the color or pattern names and it's easy to find what I'm looking for.