You folks need to forgive me on this one. This is an after the fact instructable so I will show aspects from a completed point of view.
I always wanted my home automation pc to be wall mounted to free up space and also to keep it safe from physical impacts.
The first step is an appropriately sized plastic enclosure for a small motherboard. Here is what I have done.
Step 1: Mounting the Enclosure.
Step 2: The Power Supply.
I use an M4 atx dc powered psu for my embedded automation system. I mounted this on the inner ceiling of the enclosure using plastic cable ties.
My home is solar powered so it's easier for me to use dc voltage to keep this critical pc operating 24-7.
Step 3: Ventilation.
Using an 80mm pwm case fan I cut a rectangular opening on the upper left hand corner to exhaust heat. In the bottom of the case I used a hole saw to cut three 2.5inch holes.
Step 4: The Computer.
I use a mini itx 1151 motherboard, 16Gb DDR4, with an Intel i7 6700T to provide a super efficient, power savings brain for my home automation system.
Step 5: Data Storage.
For internal data I used a ssd 1TB. To provide super fast backup of data to a redundant drive I use a 2.5inch external hot swap Bay which I stuck to the underside of the enclosure with double sided tape. The motherboard has usb3 but this has never lived up to its expectations. Sata3 gives awesome and guaranteed performance.
Step 6: Wire Management.
Step 7: External Power Support.
Step 8: Cables Access.
A 3 inch hole I cut on the right side of the enclosure to get usb, power (25/12/5VDC) and ethernet cables to the enclosure.