I built a clear case a few months ago, and I ended up not using it anyway. It was though to take the drives in and out, I had some problems with the plexi sagging in certain spots, and it took FOREVER to build. Then again I screwed mine together, I didn't glue it, but even if I had glued it, it would have still taken a long time. Also, all that plexi can get expensive, and after all the necessary supplies are bought, its going to cost over $100. And it you make a mistake, like slipping w/ a dremel for example, its very noticeable.
If you're really intent on building it though, I would recommend using 1/4" plexi, that should help avoid sagging. And you should glue it together. But, most importantly, make sure that you have a good blueprint to go by, and know exaclty how you're going to do things like put in your agp, and pci cards.
Anyway, I hope I haven't discouraged you too much, good luck, and drop me a line if you need any help
I can help ANYONE lay out the design of their case ina CAD program. Simply list off which parts you want to use (motherboard, Drives, Power supply) and if you want them in a certain configuration (Left-Handed, Desktop, Mid Tower, etc.).
I used the same program to design the layout for my clear case...
One thing I highly recommend is the use of screw assembly since glueing the pieces together is difficult and permanent. It's also helpful to use a premade Steel motherboard tray. I have one Micro ATX tray as a spare in case I need to make a new case but I'd be willing to part with it.