I understand your desire. For years, I thought of designing my own game. I have all the tools from restoring a car and building wood/shed projects. I did research the options. I found I was over my head for quite a while. I would recommend as others here have to rebuild a project pin first. That will educate you on the electronics involved vs the mechanical parts. I chose a theme I could relate to and also find a relatively inexpensive model. I would avoid EM machines, they look prehistoric under the hood. I went with a Bally/Williams WPC machine. The aftermarket industry sells lots of parts that you won't want to spend your time making, unless you are a machinist with associated tools. You can buy blank boards from DumbAss and build them yourself, by sourcing the necessary electronic components and soldering them all on, following a schematic. Yes buy a manual with the WPC or whatever schematic or download one from IPDB. Know there are known mistakes in the manuals. Building your own wiring harness is another treat (actually 3 or 4 harnesses). Wiring and Building connectors with a Molex tool and pins is a fun time to kill weeks of fun.

Just for an exercise, download the parts list from a known game. Then log onto Marcos Specialties for the same game. Addams Family for example. Then start totaling the costs of all the parts you need. Then find out than many parts are one offs and not stocked. Then go on Ebay and try and find that elusive part. Then Google the part # and find it in Australia or Argentina or Germany or UK. That is what I have been doing, price is not in the equation anymore.

I have decided to out source the cabinet and back box to Virtual Pin. Cheaper and quicker, but will buy the plain wood version, that is already cut to the right size, instead of re-inventing the wheel.

It is a fun journey though.