I started by making 24 boxes. Small boxes from the pantry (i.e. Jello pudding, tea boxes, butter boxes, etc.) make excellent templates. Just unfold them, laying them flat, and trace onto card stock. After cutting them out and scoring, I folded them into the new blank advent boxes secured with glue.
For patterns, the kids contributed drawings of snowmen and trees and I also used illustrations and print taken from old Christmas books. I didn't let the dimensions of the box limit the size of the design, most extend past the box edges.
I filled the decorated boxes with little treasures such as shells, a nutcracker to paint, mini birds' nests, tiny wood ornaments, etc.
I placed them on the wall, held in place with removable mounting squares.
This can be a very versatile project and I'm already thinking of some different ideas for next year. I'll start planning earlier in the season though, it took me longer than expected, but I'm really pleased with the results and it was fun, too!