I have used Dough's method (which I had to read 3 times before fully understanding, not being native English) for making a bellows and it works well.
Firstly, make a paper model. Make a second paper model and then, make a third. By then you should be able to make a rather well looking bellows. Don't use the real lining yet as you will be messing up things.
For the impatient amongst us, rather than drawing everything on an oversized sheet of cardboard, make a PC drawing and print each side of the bellows on 120 g/m2 paper. That should be strong enough as stiffeners.
Cut and paste everything according to Dough's instructions.
If you'd prefer to use M3 spray, no problem, but be sure to sandwich the stiffeners between 2 layers of paper and you're ready to start folding after 5 minutes of glueing. In order to see the stiffeners and having a guide for folding, I used brown wrapping paper on the inside and and a rather transparant thin layer of paper on the outside, like the one people put on tables at weddings, festivities etc.
Using a double layer of paper will help you in folding the bellows afterwards. The stiffer (but then again, not too much) the material, the easier it will be to fold. I noticed that difference between my first and second bellows.
After folding, apply multiple layers of spraypaint. I used matte black car paint and it looks good.
As stated, I used this for paper bellows. The real thing will be made soon :-)