Wrap boxes in black wrapping paper.
After measuring wrapped box, figure what size square will work, and cut 54 squares of the six different colors of card stock for each cube you are making.
I did not do a lot of precise measuring. I put one square of double stick tape on nine spots of each side of wrapped box, and then began lining up the colored card stock cut squares.
I made a variety of sizes that will be table decorations for an 80s birthday party.