The EFFEKTIV units from IKEA are deep enough to hold the 12X12 paper holders, and the shelves are adjustable so height isn't a problem.
I used a Cropper Hopper Paper Holder for each color.
And inside each one is the smaller "project" holders that holds that colors scraps. I can really see me using my scraps more this way as they are so easy to get to. And they are easy to file the scraps when cleaning up after a project.
I also had plenty of dividers so I've placed a divider in each CH and have paper (or lighter weight cardstock) on one side and cardstock on the other.
And then above that are the other two shelves. The middle one is just tall enough to hold my Iris container that has a stack of papers that I found at CostCo or Sam's some time ago. Then the top is my 12X12 stacks, magazine holders on their sides holding Vellum, Transparencies, GP White Cardstock, and a small CH holding some of my smaller stacks and packages (like freebies from Archiver's).