Mini ITX, Low profile CPU cooler or LC, Maybe mount HDD and SSD on top or sides, PSU can fit if you choose a short GPU such as R9 nano, and dont forget that you will need some sort of acting cooling system blowing through the chassis.
I wrote this many years ago, it got top comment on a really old one of his cat videos. Had like 400 likes before the YT comment system changed and screwed everything up:
Linus' oven is overclocked to 350*C. His microwave is overvoltaged and his fridge is liquid cooled. Oh, and his stove has tubo-boost with surround multi-pot support. All his appliances run in SLI. His car does not have a key, but a power button instead. And finally his vacuum is fully modular and causes a positive air pressure inside his house.
found on the internet years ago:
Until I get round to installing a SSD, I'm using a rotating wax cylinder taken from an early phonograph set. The apparatus is housed in a large five story tower. Cooling is provided by a constant flow of methylated spirits. I've incorporated a hashing function which is sometimes disrupted by a family of bees which have taken residence in the third megabyte.