So this is isn’t really MY idea, I think I saw something similar on Pinterest, but I did give it my own twist. I’ll explain what I did and you can try it yourself!
NOTE: I choose a house for a shape, but you can use whatever you like,
as long at it has to straight sides so you can tape them together.
First I cut out simple house-shapes from cardboard. Thick enough so it can stand up on it’s own, but not too thick so you can’t cut it anymore. I liked that the houses had various sizes, but you can of course also cut them all the same. The most important part is that they have the same width. This way they will nicely stack on top of each other when you’re done. You can cut out as many as you like, just keep in mind that about 3 cm is the maximum for a mailbox.
Next I decorated the houses with stickers, scraps of paper, old maps, anything I had laying around. You can use anything you like, just don’t make it too much 3D or fragile, or else it will damage when you put it together (and that would be a shame!)
Then I but the little booklet together. I placed the houses next to each other, leaving a little space in between (about 3 mm) and put a bit of masking tape on them. Front AND back. By leaving some space in between the houses when you tape them, you can fold the houses on top of each other. How much space you leave in between them, depends on how thick the cardboard is you are using.
To close up the booklet I used a button and thread. On the first house I sewn a button and on the back I put a piece of thread (knotted on the inside) through the house. You can cover up the threads on the inside by just putting a piece of tape over it.
You close the book by zigzagging (left, right, left, right, etc.) If you don't understand what I'm talking about, see the picture of the end result).
Next I taped in little (flat) goodies. You can fill it completely, but that's not necessary, I put in about 8 things (including the letter).
AND THIS IS THE END RESULT
I hope I've explained it well enough! If not, just leave a comment with a question.