I've made my own tapered bellows design out of black thin cardboard. What I did was meisure the lens plate and groundglass plate. I used twice the focal length for the unfolded length of the paper. Then I drew 4 connected trapezoids with the lenghts I previously meisured. (actually, I cut the first and last trapezoid in half for better connection.
Now comes the tricky part. Make a zigzag line of 90 degrees in the middle of the intersecting lines. I used a zigzag with a 2cm offset. The zigzag lines are supposed to be the mirror image of the next intersecting line.
Next, I used an empty ballpoint pen to make indentation lines in the cardboard. This would be the folding lines. Than I taped both ends of the half trapezoids together and started folding. The first couple of folds are a bit hard to do, but along the way it gets easier.
A square bellows is easier to make, but won't fold as tight as a tapered one. The first bellows I made was a tryout for a better, more durable one.
Have fun building and exploring how bellows work.