This is the system I use to create enclosures for many of the electronic prototypes I create. The Illustrator file is based on the P2 template from lasercutting service Ponoko.
The system includes an 84mm x 84mm baseplate as a starting point but also includes mounting templates for Arduino, Adafruit Permaproto boards (very handy), a 16 x 2 LCD and a few other things. Mix and match and add to it as you need.
The cut lines are 0.01mm in width, set to 0,0,255 RGB. All holes are designed to use M3 bolts / screws. Use the system as a starting point to build whatever you need.
Distributed under the MIT license.