Revit under Parallels is A REALLY BAD SOLUTION. It's one of the most demanding applications you can get, and you are proposing to run it under another operating system running in OS X.
This means that in addition to running OSX and other applications, you are running another application which simulates an entire Windows machine, and on top of that you are suggesting running Revit!
Parallels is a good application, it's fast, and virtualisation software is very useful. I use it on my dual Xeon 8 core Mac Pro with 20Gb RAM, but performance isn't what you would call stellar! Natively it runs Archicad, Vectorworks and SketchUp beautifully, and with complex models.
I wouldn't consider running BIM on my VM though. The fact that it works is fine, but what happens when you start to work on anything other than the simplest model? Whatever the minimum hardware requirements for Revit, you would need a significantly more powerful machine to run it in a Virtual Machine.
Given that currently high end Macs for demanding 3d work are a bit of an expensive joke, it makes no sense at all for Revit.
When the new mac Pro is introduced it may be a different situation, but I suspect you may as well pull a big pile of money out of your wallet and set fire to it!
In practical terms, if you want/need to run Revit, you need PC hardware natively running Windows. Bootcamp is unquestionably the best solution, but you effectively abandon OS X and move to a Windows environment.
Forget the Mac if you want Revit.
I have been a Mac user for a long time, and they are fantastic for all sorts of things - but not Revit...