Building from scratch can be a fun experience. However, if you're not used to woodworking, it can be daunting. If you don't have the tools, you'll also have to outlay the money to get them as well.
Using an existing cab is good (as long as it's either a generic cab, or an empty cab that finding the parts for would be hopeless) as there's little to be done, other than rig up a control panel and install electronics.
Control panels vary from person to person. I don't like cluttered panels, and design as such. Like choosing a list of games that get along with a certain kind of controls, like a 2 way joystick and a single button runs Galaga, Galaxian, Space Invaders and the like.