There are two possible ways to create a new Pattern in GeneXus X.
One is to manually define and develop all the necessary files.
If you want to develop a new pattern by creating all the necessary files, you should follow the steps below:
Create a folder called <PatternName> under <GeneXus X Directory>\Packages\Patterns, containing the following files:
Here you can see a step by step sample.
Another way to create new patterns is to use PatternBuilder wizard (available from GeneXus Platform SDK Upgrade #3) that simplifies the creation of the pattern, the templates and XML files. Here you can see a sample using PatternBuilder.
A final option is to "fork" from an existing pattern. Here are detailed the necessary steps, using the Work With pattern as an example.
Check the following workshop material from the assembla site.