This was suggested to me from someone who saw the Stars and Stripes.

It is best done on cardstock, or onto quality paper then glued to sturdy card before cutting. You may also want to add a house number and family name to the side using your graphics program.. the original had a roungh scrawl and looked very country-ish.

Assemble the the mailbox first.. the bit sticking up at the top is the roof, which folds over the curve of the sides. There is plenty of extra space on the end of this to use as tab to stick tothe opposite side. You may want to add tabs to the curves as you cut, so that you can stick the roof to them and make a better join along it.

The flag is cut out and folded in half. Either use the piece of red (if it's on sturdy card) or a piece of fine wood etc. as the pole. This is caught at the folded end of the flag when you glue. That is then glued to the side of the box.

The whole thing then needs to be attached to a piece of dowel and a flat base, or however you want to use it.