I have been working on this build on and off for a long time now and it is finally in a state were I want to post it. It is about as finished as it will ever be, because with projects like this there is always tweaking to be done.
Currently the PC hardware is:
CPU/Motherboard cooler: EK-FB ASUS Z270E Strix RGB Monoblock
GPU: Gigabyte AORUS GTX 1080 Ti Waterforce with liquid metal form the previous owner
Motherboard: ASUS PRIME Z270-A
RAM: G.SKILL TridentZ 16GB 3200 MHz
PSU: Corsair AX1200 Gold (from a very old version of my PC with 3 GPUs)
SSD: Samsung 970 EVO M.2 1TB
HD: Three random drives totaling 11 TB
Now on to the interesting part of the build. I build the case from 1 inch and 1x2 inch square steel tubing with 16 gauge sheet steel for the panels. Originally I was just going to use 1 inch square tubing at the front and back of the case with the sheet metal connecting them. However that turned out to be surprisingly floppy, so I ran two pieces of square tubing top and bottom to sport them. I had ran out of 1 inch tubing at this point and the place I get my steel from was out of it too, so I got 1x2 inch tubing for the rest of the build. This did not help with the weight of this beast. For the back panel carving out the holes for the I/O plate, PSU and GPU was not too hard, but the fan mesh took forever. I had to drill something like 100 holes in the back and then I used a countersink bit on each side of hole to clean them up. I bought a cheap drill press to help and it was still not fun. The front mesh went a lot smother once I figured out a good source for the mesh. I ended up using a gutter guard I cut up to give access to the two disk drives and card reader. I tried welding it in place at first, but it just kept melting and a bunch of set taping screws turn out to be a much better way of attaching it. I made a motherboard mount out of 1/4 inch steel bar that I welded to the top and bottom of the case. The mount its self was not too hard to make but tapping the hole for the tiny standoffs was a nightmare. In total on the case I think I had to tap 13 of those holes and I think I broke 10 taps doing that. Those taps are not designed to be used in sold steel. To mount the disk drives and card reader I made a little cage out of 1/4 inch bar steel and a strip of some bendable flat bar. For the hard drives I just bent two "U"s out of the flat steel bar and weld that to the bottom of the case. To mount the radiator I welded two bits of square tubing to the bottom of the case and bent two more "U" out of the flat steel. I screw the flat steel over the radiator to hold it place. Both side panels are just big pieces of sheet steel I cut to size and welded quick release hinges to one side and have two bolts hold the other side. They can swing open and be removed easily to get in side the PC. For the window I just cut a big hole in the side panel and bolted a piece of acrylic I found to the inside. I used way more bolts than I needed because I though it look cool.
For the water loop I used a copper/brass radiator out of a 1978 Chevy Nova. I found adapters to take the hose size down to 3/4 inch right out of the radiator. It then goes through the top of the case to a seconder heater core water pump out of a BMW Mini. To power the pump I got 12v form a moxel connector that I feed into a speed controller. The power then goes to the pump which I have mount to the underside of the top of the case. There is a potentiometer on top of the case so I can control how much the pump pumps. This turned out to be really useful for beading the loop because I can't turn the case on its side to try to get the bubbles out. At full tilt the pump can just power force the bubbles out and I can turn it back down for normal use. After the pump there is a 3/4 to 1/2 inch adapter. Then it goes in to the CPU followed by the GPU. Then there is another 1/2 3/4 adapter before the custom brass reservoir. I made the reservoir out of a sheet of brass. I bent it into a cube shape with no top and use copper rivets and solder to seal the sides. I put two 3/4 connectors on the sides for the inlet and outlet. I also put a barb on the side for bleed port of the radiator, but that turned out to be useless. On top I used an aftermarket bleed screw for an e36 (90's BMW 3 series) has the fill hole, because that is my first car and I love it. I though it would be a nice little touch, but filling from the reservoir turned out not to work. I ended up adding a fill port to the top of the tube that runs between the radiator and pump. I also put a drain valve in right after the GPU after an expensive lesson I got while trying to drain the loop. That cost me a GPU.
To turn on the PC I put a key on top to keep with the automotive theme. I can also start wirelessly it with a key fob I leave on my desk. On top I also have a display that show the water temp right before it goes in to the CPU.
Today I ran a stress test to get temps. Nothing is currently over clocked and the CPU bounces between 62 and 72C while the GPU peaked at 34C. That is after a 15 test with both the CPU and GPU being hit. I think I would need to delid the CPU to get the temps down. I am happy with the GPU temps but the CPU temps are disappointing. The radiator is passively cooled. I have be using versions of this PC for a long time and I never see the radiator pump out much above ambient temp water.
Here is a link to a photo album with a bunch more pictures of the PC. https://flic.kr/s/aHsmMe6yqf