If you are asking about UI Automation properties for the Start Screen then it is using standard patterns. You can look at what is there with Inspect.exe from the SDK.
If your question is about writing your own automation app using UI Automation please see the
Windows Desktop Development for Accessibility and Automation forum. You likely will be better off using the native UIA objects rather than the managed ones, even if you are calling them from C#.
This post in that forum discusses how to do so and points to some samples demonstrating it. That said, I'd expect the C# automation app to be able to see the Metro style app: double check that both the C++ and C# apps properly signed, manifested, and located
for UI Access.
For questions on Coded UI and Visual Studio Test tools please see the
Test Tools in Visual Studio vNext forum.
--Rob