Adding a new table to the system catalog

I am exploring and poking at the source code to inform a design for adding valid-time support to postgres.  The feature will required updating existing system catalog tables as well as adding one or more new tables.

Is there any documentation on how to update the system catalog?  What files need to be created/updated?  Do I need to run any utilities for generation manually or is this done as part of the build?  How do I assign a new OID?  

Thanks in advance

Paul