Hello,
Please take a look at these two documents and let us know if you have any specific questions.
Custom automation peers
http://msdn.microsoft.com/en-us/library/windows/apps/jj219211.aspx
UI Automation Overview
http://msdn.microsoft.com/en-us/library/windows/apps/ee684076.aspx
I hope this helps,
James
Windows Media SDK Technologies - Microsoft Developer Services - http://blogs.msdn.com/mediasdkstuff/