The first thing you’ll want to do is order and print all of the necessary components. The printed components are all available on Thingiverse here. On the motion sensor, I included slots for both zip-ties and holes for screws/nails

For both boards, I used small PCB proto boards I had handy. I assume they’re standard sizes, but you might need to adjust the models accordingly. For other projects, I’ve put together wiring diagrams but since this project is so simple, I didn’t. If you decide to make it and would find a diagram helpful, let me know and I’d be happy to throw one together for you.

With the finished boards and the printed enclosures, assemble everything. 

Obviously, there are countless way to skin this particular cat. Since I have no painting skills myself, I’ll leave this to you.

The code is located on Github here. It’s written for Particle Xenons but should be easily edited to work on a similar Arduino.