How to build a computer cabinet with proper ventilation

First: set up your devices in a cabinet

Set up your computer in the cabinet. Wire everything.

Raise HDDs using LEGO to have a better airflow

You can add heat sinks to small metal cases. These will enlarge the surface of the case and enhance cooling. As you can see, I also put a notebook cooling pad under my Mac Mini.

Second: Modify the door (you can also modify the cabinet, but doors are easier to replace)

For the door you'll need to saw out holes for the fan and the ventilation slot

Put a dust filter over the fan hole and put the ventilation slots in

Add hinges so the door can be opened later

Make sure that the fan blows air into the cabinet, not out

Screw the fan to the door

Screw the door to the cabinet

The fan will suck in cold air, warm air can exit through the ventilation slot.

Through the vent you can also see your HDD status if you place them right. On my Lacie, blue is good, red is bad, so everything is okay

And: You're done