This is such a great idea. One I may just use in my daughter's room one day soon. Especially since I know she'll spend hours upon hours stacking and restacking them.
How easy can this be? Grab a pile of Ikea Prant plywood boxes, in varying shapes, however many you want, paint the inside whatever colours you want, and stack accordingly!
I absolutely love that these are held together with binder clips! Genius!
all photos - Livet Hemma Blog, Ikea Sweden