If you’re starting out with materials in max that are not vray materials then I believe first you need to convert them which you can read about here :
But to export to .vrmat there is an option to “export VRMAT from scene material” This then will create those materials in whatever directory you want which should be loadable into revit as .vrmats. I don’t know what menu this is under so you can either search for is with ‘x’ or add it to a vray menu you can create within max.
I think the .mat format is 3ds max’s core material format which can represent any material that you make within 3ds including materials for other render engines. .vrmat is a more specific file type which, in max, can only be exported from a material that is under the vray rollout in the material editor. It’s Vray’s proprietary format essentially. The reasoning for this would seem to be for users like yourself to exchange exact materials between 2 software you are using vray inside of rather than having to worry about revit, max, modo, and blender using the same material system since they’re not all made by the same companies. (This is my understanding so if anyone has a better or more accurate explanation feel free to correct)
For getting VRMats I would say flying architecture is a really good one that I trust and has a easy website to navigate with a solid material library. I don’t know about whether or not they’re physically based but they look really good.
I recommend you to watch first our quick start tutorials here: Chaos Docs
V-Ray for Revit help page is currently under development. However creating materials in V-Ray for Revit is quite similar to that in V-Ray for 3Ds max, so you can read about it here: Chaos Docs
You can also browse on youtube where many 3D artists share different approaches.