I built my own MAME cabinet a few years back (wow 11 years ago now - time flies). It was a really fun project. Honestly, it is just a PC with an interface that takes the place of the keyboard. It isn't as daunting as you might think.
My biggest challenge was building the cabinet and control panel, I built mine from scratch instead of sourcing a used video game cab and re-working it. That gave me the flexibility to have lots of buttons, a trackball and a spinner.
I'm happy to help, PM me or shoot me an email direct: jholmgren at gmail dot com.
Here's some pics I took during my build:
http://www.littlebluespitfire.com/gallery/main.php?g2_itemId=2245Jim