I belong to a online group that sets a challenge each month from the book below
Some are not easy and certainly set the challenge.
The original size was cut the sheet 9" x 12".
I decided to do 12" x 15".
The sizing can be made to suit by using the ratio 3:4
The Diagonal Pocket, despite following the easy folding instructions of 20, hit a road bump at folds 18 and 19. I was very fortunate to be sitting with a lady at quilting guild who does origami.
I chose one of the sheets of paper that I bought at Kyukyodo stationary shop in Tokyo.
It folds into a pocket with the diagonal pockets allowing small cards, notes etc to be inserted.
A comment I received, it could be used as an envelope for an invitation.
Finished size 4" x 6".
I added 8 pages to the centre, sewn by machine for a notebook.