Step 1: What you need
Step 2: Build the box
cut 2 square dowels the width of the finger hold planks...pass it through the box to make sure it would fit...then fix it at the bottom...you may glue,nail or do both!
Step 3: The Fun Part- Texturing and Painting
For more ideas on texturing check out the below instructable
Paint and decorate how you like...I of course went for the rainbow colors.
Cut numbers in a mirror sticker and paste on one side...you can put on the other side pictures of what you want inside the box
Step 4: Ta Da!
Step 5: Some Rainbow Thyme Ideas
Coat rack http://www.instructables.com/id/Personalized-Mosaic-Coat-Rack/
Foam Wall decor frames http://www.instructables.com/id/Foam-wall-decore-and-frames/
Rainbow book shelf http://www.instructables.com/id/Build-a-READING-RAINBOW-Book-Shelf/
Bulletin Board http://www.instructables.com/id/Bulletin-board/