Creating Master Pages
Create Master Pages and turn them into page layout templates
You have two options when creating and editing Master Page based templates in C1 CMS: in your developer IDE (e.g. Visual Studio) or in the Layout perspective in the CMS Console.
To serve as standard C1 CMS Page templates, Master Pages must be created in ~/App_Data/PageTemplates. Besides, they must include some minimum markup/code to be recognized as C1 CMS Page templates.
When you create Master Pages in the CMS Console, C1 CMS takes care of creating required Master Page files (master and master.cs) in the proper folder and adding boilerplate code. However, if you want the IDE features Visual Studio provides such as IntelliSense, statement completion or write-time compile warnings, you should choose to create a Master Page in Visual Studio. And using the Visual Studio 2012 extension CompositeC1WebFormExtensions.vsix, helps get the required code/markup immediately. (It works with Visual Studio 2012 only.)
Both options are describe here for your convenience:
Using Master Page based templates
Using Master page based templates is no different from using any other type of the C1 CMS templates. The editors deal with "C1 CMS Page templates", and technology "behind the scenes" - whether it is XML, Razor or Master Pages - is absolutely transparent to them.