I would love some instructions for that one, too, Dominik. Looking at your
Flickr and
website, you have a lot of excellent models.
For
Master Frog, the €5 banknote is 120mm x 62mm, so any 2:1 sheet of paper would be very close to the right proportion.
Using the visible parts of the model as a reference, and the fact that it looks like it's divided into 8ths both ways (can you confirm this, Dominik?), I created a sloppy version. It looks similar, except that it doesn't hold together very well/at all. Some locking mechanism(s) would be needed to keep it all tight. The lid is pretty solid, but the front of the "body", and the central part, is rather loose.
Also, Nick Robinson has a lighter (seen
here, third image down). Details of where to find the diagrams are under the picture;
OUSA 1989 and
Best of Annual Collections 1981-95.
Gilad's pages on each book (click the links under the picture as mentioned above) give details about the models in each book, as well as some notes. They might be worth checking out, rather than paying $14/20 for the book for a single model, you might be able to find other models in one or the other book which would make it worth the price.
Each page on The Source site has a PDF of contents, with pictures.
I may take this as the chance to work on my own model.