We get asked about using Revit on a Mac using Parallels quite often. According to Autodesk's system requirements page for Revit, it's a supported setup. Here's my problem with that. Parallels is a virtual machine and the virtual machine cannot access the graphis card of the Mac. Parallels provides its own video memory. You can increase it up to 1GB. However, since there isn't a driver for Revit to recognize, you're not going to be able to use hardware acceleration, and you'll have to run on RAM only.
The other thing is that as of August 2017, Parallels doesn't support DirectX11. This can cause hesitation for some Revit users. If I'm going to be using Revit a lot, it's just not worth the price of a Mac computer, Windows OS, and Parallels just to have Revit kind of work, but not well. If Revit is your primary software, get a PC.