Hellu!
A while back I made this leather cover to fit a couple of A7 notebooks, also knows as travelers journal. It's made from scrap-leather, I did no sewing, the piece on the flap is glued on and the curved edge was from before. I just removed the stitches to fit the bottom leather under the flap on the inside.. I realize this barely fit as a leather craft, I hope it's okay anyway!
Sounds like a great project, you should definitely do it and keep us posted about it! If the community can be of any help let us know :)