It is constructed entirely of cardstock. The white is actually glitter cardstock, which is tricky to work with because nothing sticks to it! That's what made me think to use brads to hold pieces together, and that worked out great. I used the Xyron Creatopia to stick several pieces of cardstock together to make the pieces sturdy.
The front door has a flap on the top that folds over a post I poked up through the top arch of the box. This keeps the door shut, but makes it easy to open, too. We decided to make the mailbox look like a truck, so we added some accessory pieces, like wheels and front & back windows.
I'm really pleased with how this turned out, considering how unsure I was about this project in the beginning!