Here's a little decision making "checklist"
I was going through...if if helps you, use it.
Also, I am choosing upright, so this is for an
upright. All others can be added by others
who have built them.
Formfactor
Upright
Cocktail
Driver
Other
Size
Standard size
Mini size
Coffee Table
Cabinet Design
One-piece Design (standard style)
Two-piece Design (gotham-style)
Three-piece Design (megalo-style)
Coffee Table
Video
Computer Monitor
Arcade Monitor
TV, Projector, etc.
Video Design
Attached Monitor (cabinet-style)
Detached Monitor (megalo-style)
Control Panel Setup
Single Control Panel (all-in-one)
Multiple Control Panels (interchangeable)
Player Qty
1-2 player machine (pac man type)
1-4 player machine (nfl blitz type)
"Fancy doo-dads"
Sound (speakers required)
Lighting (marquee, coin doors, etc)
Finish
Paint
Stain
Laminate/Formica
Other
Controllers
Button types
Joystick types
Trackball(s) (and type(s))
Spinner(s) (and type(s))
Light Gun(s) (and type(s))
Wheels/Pedals (and types)
Dance Pad
Computer Interface
I-Pac type
You-Hack-Pac
OS
Windows
Dos
Linux
Other
Machine Use
Single Game
Specific Game(s)
Front End for multiple games
Computer
(specs depend on the above decisions
made and should handle everything
you wish to do. If making this
decision based on "what I have lying
around", plan to be able to use it
for the bare minimum. By setting your
goals low, you will be pleased if
your machine far surpasses what you
wanted it to do!)