I used plywood underlayment (from Lowes) for the boards - you can use acrylic if you like, or any other laser-safe material.
4 pieces - 1 inch #4-40 aluminium hex standoff
12 pieces - #4-40 3/8 machine screws.
4 pieces - nylon washers.
Here is my design for the platform - I designed it on Adobe Illustrator, but a suitable free alternative is Inkscape, which I really like too.
Step 1: Laser cut the parts
Easy, peasy, japanesy! Well ... almost! (see my Notes below).
Here is the YouTube video showing the laser cutting - the original time was 6:05 minutes, but the video is sped up to condense it to 46 seconds. - http://www.youtube.com/watch?v=l9wLE9ftEYo
1) Set the line width to 0.01px in Adobe Illustrator to set it to cut.
2) Set the page size in the print settings to the actual page size in your Illustrator drawing (in my case, 24x18, even though the actual used space is much less) - the printer is very sensitive to this, and would not do anything with my print job otherwise.
Step 2: Assemble the parts!
You can have the Arduino Platform on top, or the Companion Platform on top - your choice.
Screw the top board on to the aluminum standoffs using the machine screws. Place the standoffs on the bottom platform, and repeat the process!
The cut-offs allow wires to be routed from the top layer to the bottom layer.