In the unlikely event you have missed it or just to complete the hit list if you search for examples on this blog, the Build On State Change Work Item Save participant/follow up action is a complete example as part of the Rational Team Concert Extensions Workshop.
The Build On State Change Work Item Save participant monitors work item state changes of configured work item types and state changes. If a qualifying change happens, it issues a build request for a configured build definition. The example comes with a complete package including the configuration UI.
Just Starting with API work?
If you just get started with extending Rational Team Concert, or create API based automation, start with the post Learning To Fly: Getting Started with the RTC Java API’s and follow the linked resources.