xamarin-android-schema-generator is an Android layout.xml schema generator.
WARNING: Android layout xml does not fit well with XML schema restrictions. XML Schema is not extensible enough to accept non-standard components nor non-standard attributes which are (still) in android XML namespace (due to the limitation of element/attribute wildcards). So, you CANNOT use the resulting schema to VALIDATE your layout xml resources. It should be used only for auto-complete element/attribute candidates.
To generate schemas, run the tool with path to Android SDK:
mono xamarin-android-schema-generator.exe /path/to/android-sdk-(os)