In the final Community Tuesday offering. Joe from Big Huge Games has released a collection of documentation and examples, which I have separated into "kits" to make the downloads a bit more manageable in size.
This is the ROL Custom Tribe Kit. Described how to create a custom tribe to add custom units/buildings to maps, with basic and advanced features. Also contains a file which shows a sample custom tribe with comments on how fields can be modified. Enjoy!