I wanted to build the smallest possible gaming machine so I set out to find the smallest possible mini-ITX case. The Silverstone SG05 is literally the smallest case that will fit a 2 slot standard GPU so that's what I went with. The case requires a SFX form factor PSU only so I went with the largest wattage available - only 450 watts.
The build was really cramped and there was pretty much no possible way to manage the cables. Everything barely fit. CPU temps get a bit high under load (72 C) and on 100% load with prime 95 go up to 82C. I'm a bit worried. GPU temps are wonderful even on 100% load.
For under $800 I think I did pretty well.
CPU: I need a low power consumption cheap i5 so I went with the i5-3350p. Picked up an open box (but never installed) one on e-bay for $130.
Motherboard: Cheapest motherboard with SATA III and USB 3.0 Can't overclock in such a small case so I got H77 instead of Z77.
Memory: 8 GB of 1600 Mhz is the sweet spot for a budget build.
Storage: 120 GB SSD as a boot drive and a 500 GB storage drive
Video Card: I wanted to find the best performing GPU that would fit in this case (10 inch length limit). I thought a 7950 was out of the question since they were all over 10.2". Then I came across this particular 7950 that is only 9.4"!! It is the only 7950 under 10" that exists. The only better GPUs that will fit in this case are a 7970 also made by XFX that is under 10" and a GTX 760 but I ruled these out as they cost $50-80 more than a 7950.
Note this is the GPU listed in the build is not the one I used. It is the XFX DD Radeon 7950- TDKC. PC Parts picker doesn't have that particular model though. Price is after rebates and selling the Radeon Gold rewards card for $40 on e-bay.
Optical Drive: Case only fits a slim optical drive. You make sure to buy an adapter for it if you're using this case.
OS: Got a Windows 7 key off e-bay for $50