You'd have to scavenge a case for the buttons, switches and ports. You can probably pick up a cheap case with the items you need for $30-50. For spacing, just measure the same cheap case. I've tried making my own aluminum case and gave up. Still have the bare carcass about 4' away from me right now. It's a lot of work.
Probably easier to just buy one. For HTPC, more and more cases are available.
Aopen DeskTop mATX Case Model H340D Black w/ front USB 2.0
I actually have this $37 case and it's pretty nice for the money. There are front USB 2.0 ports as well as audio ports. It is black with plastic feet on the bottom so it may fit in with other equipment. It is decent quality, using reasonably thick metal. It is narrower than regular stereo equipment, kinda like many of the VCRs that are on the market now. It will also be deeper than other equipment. The case only takes mATX boards (or flexATX). It comes with a proprietary power supply that puts out only 200W but seems to be quality and is very quiet (pretty much silent). Two things I don't like about it are #1 the external 3½" drive bay has a floppy drive slot/face on it. I'd prefer just a standard blank since I don't think I'd be needing the FDD. #2 the expansion slots are not full height. This makes for a nice low profile case, but good luck finding cards that fit. A good choice for a home theater setup would be one of the new/upcoming mATX NForce2 boards with integrated 5.1 audio and integrated TV-out. That way no cards are needed.
Antec Media Center Case, Model Fusion
This upcoming $110 case looks promising. There are no detailed pictures yet (and I just checked
Antec's web site and didn't find it) but the one picture at Newegg shows a nice black case with silver accents, front panel ports and feet that matches most stereo equipment. Though it's expensive, it comes with a TruePower 380W power supply (worth a bunch on it's own), has many drive bays (some with rubber grommets to decrease HDD noise) and supports regular ATX motherboards. It will probably match stereo equipment in all dimensions except for greater depth.
I am SOOOoooo tempted to get the Antec case when it becomes available, even though I just got the AOpen case (for $25 on refurb, hehe).