I used wood, a crank and shelf braces. The size of the main board is 70cm x 40 cm, probably a bit too big. I used 20mm thick pine wood and also a bit of plywood for the thinner parts.
I won't give the complete build instructions, the pictures are self explanatory, and also this is just the prototype, the final project will be laser cut and I will publish the files here.
The only tricky part was to get the mouse wheel to touch the crank with just the right pressure. At first the contact was orthogonal, which was a bad idea, because if the wheel is not exactly placed there is too much pressure on it and it falls. So instead,
I just positioned the wheel like I would have for a regular gear. I still use the plastic base of the mouse, I just saw off as much as I could of it.