[Witchdoctor]

Here is a quick sketch up I mad should be able to get all this stuff at a local hardware stire

you can make the demensions anything you would like.

I would make the bottom wide enought foe a PS on it's side

overall about 4" wider than the board long ways and 7" longer short ways so you have room to put some cable managment holes in it for power, SATA & PCIe cables

once it is all drilled and ahols cut paint it up before you assembel

3/4" U channle may be better if you can get it for you card hold downs

Good luck