I've been re-casing my A1200 over thep ast 2 months, bit by bit as time allows.
I decided that a Mediator wasn't worth the money what with the impending A1 boards, and as long as I got a Scan Doubler, I'd be ok in the short term.
So, not wanting a Mediator, meant I could put it into a desktop case, and I had an old Sun Sparc20 case lying around that would do the job. I can safely say that it HAS done the job and looks absolutley spiffing. :-)
You'll definately need another PSU though, and this is where I had my most major hurdle, because I was using a deskop case, the PSU is outboard, and PC PSUs arn't really that safe un boxed, So I ended up completely stripping down a PC PSU, and reboxing it using the existing Amiga Power cables and switch! It looks OK, but not what I had originally planned.
Good luck with your rebuild, I've really enjoyed mine, I hope you enjoy yours.
-Jar.