Read original post by Diederik Krols at U2U Blog
This article describes how to build custom WinRT Metro controls in C# and XAML, with the Developer Preview version of Visual Studio 11. WPF, Silverlight, and WinRT Metro have two ways to roll your own controls: custom controls, and user controls. User controls are composite controls that are created by dragging and dropping other controls onto a XAML surface. They are nothing more than content controls that are optimized for design-time use. User controls are typically for sharing within an application, but not with other applications.