Here's a great in-depth build report from a steampunk mouse project in Custom PC:
I'd decided to use mahogany for the mouse body to give it a satisfyingly rich colour that would go well with the brass I'd be adding later. I bought a 1/4-in sheet of wood (picture 3), measuring 3in wide by 36in from a Hobbies shop. Using what was left of the mouse base and PCB as a template, I cut a hole in the wood with a fretsaw, and then sanded it for a snug fit.
Sorting out the scroll wheel came next. It was constructed from clear plastic and illuminated by a blue LED (picture 4), which wasn't exactly appropriate for a Steampunk-themed design. I desoldered the LED and used 22mm copper heating pipe to fashion a new wheel. I cut a very short length of the pipe (around 7mm) and carefully smoothed the edges using emery cloth on a flat surface. The 'wheel' had to be gradually reduced in diameter until it was a snug fit, before using Araldite to glue the two parts together. I used a Dremel for most of this work, before sandpapering it to finish it off.