I am currently in the planning stages of a "case from scratch" mod. I plan to use metal and acrylic in the construction. I have figured out how to account for the functions of most of the standard case components, however I have not been able to come up with a good way to support the rear of the PCI/AGP cards. I just cut out the section from a pre-fab case I suppose, but would rather build everything myself. I have searched the forums and read Captain Slug's post on "from scratch" mods, but haven't found anything on this particular topic. I would love to know how this component has been handled.
The most common approach to that is cutting a hole where the PCI card will go. Make it long/narrow and file the end until the card fits just snugly.
I would take the parts from a pre-made case. Most cheap steel cases have it pop rivited in place. I took one off a case that was all dented etc to put on one of my projects. There is no way you can get that level of detail on something you make yourself without spending far too long on it. And that time is better spent on other parts of the case
well, if you want to see a custom made pci rack, check out the clear cube link in my sig below. I was originally planning on using one from an old AT case, but that didn't work (error on my part), so I made my own. the only thing it doesn't have are the little slats between the cards on the back panel, but that's not really a bad thing. its only a matter of measuring and then tapping the piece that the screws for the cards go into. I also notched the piece on the mobo side so it would hold the blanking plates securely in place. It can certainly be done (yes, it will take more time than slapping a scavenged pci rack in there), but IMHO it will look much better in the end. good luck.