Hooray! I just finished making my first camera bellows and I'm very pleased with how it came out. It's for a wetplate collodion camera I'm also currently building.
The bellows is a square design, 9.25" inside and 11.25" outside with 1" wide folds. It extends easily to 24" and compress to under 2".
I'm thinking about writing a webpage illustrating the construction process for a square bellows if there is any interest in such an article. The other sources I've seen online and in books or magazine articles are all for building conical bellows.
Here are some pics showing the bellows extended and compressed, with the foamcore form I used, and with a 35mm camera for scale:
bellows and form