I've been using Gradle more often to build projects including TeamCity plugins so I created a Gradle plugin to help support the development of TeamCity plugins.
The plugin adds the JetBrains Maven repository to the list of repositories to search for dependencies, it adds the Server or Agent APIs to the dependencies. It also provides tasks to download and install a TeamCity distribution, to start and stop the server and default build agent. The samples directory contains samples from a simple server side plugin to a multi-project plugin to an agent tool plugin. The code can be found here https://github.com/rodm/gradle-teamcity-plugin and the plugin is available on the Gradle Plugin Portal.
Some more examples on using the plugin can be found in the ‘gradle-build’ branch of the TeamCity.SonarQube plugin
https://github.com/rodm/TeamCity.SonarQubePlugin/tree/gradle-build and in another project for repackaging existing tools as TeamCity Agent tools here
If you have any problems or feature requests please raise issues at github