I love this idea and basically, it's just stealing the pattern from an envelope you already have.
I used a regular sized one, but realise (now...) that there are more possibilites if you choose to make smaller ones (that tiny cute ones). Just because then you can use any paper for example from magazines. For the regular sized one, you'll be needing more paper than a normal magazine page. :/ That's why I used gift wrapping paper.
|As I said, an unfolded envelope is enough for your pattern.|
|Transfer the pattern to your favourite paper|
|Glue it together on the excess paper|