Bah, it's not as tough as they're making it sound, it might come under the heading of "advanced modding" but it is far from impossible. The biggest problem you'll have other than getting the measurements down is the cutting, there are special drill bits and jigsaw blades you can use for working with acrylic that'll help, you should also wear gloves at all times when you're working with the acrylic. But as far as conforming to ATX standards, well, that's not a big deal really. You'll have to build a drive cage that'll hold the drives, just drill your holes in the top and bottom of the case at the proper distance and you'll have that down, drilling the holes for mounting the drives isn't so hard, just make slits, then you can adjust the forward/backward positioning of the drives so they fit right. Measure the height and do some dry erase marking to note the proper placement for the vertical spacing. The next problem will be the rear openings, that'll be hard. But impossible? Nah, I don't think so. You could either fudge it and use one that already exists for a acrylic case or, just take your time and cut carefully but it can be done. But this isn't the best place to go for help with these kinds of problems. This site is more of an overall computer site, you should visit some of the modding sites, like case mod god, pheatons and so forth. I've got links to several of the better modders sites on mine, http://www.infinity-customs.com
though I don't recommend my own site, my forums are dog dead. Casemodgod.com has very active and friendly as heck forums though. You could get a lot of help there.