Our environment is a TFS 2013 server (12.0.21005.1 Tfs2013.RTM) which was upgraded from a fresh installation of TFS 2008, with a number of team projects and developers.
Here's where to find the security settings for build definitions.
TFS 2015 UI: Go to the Build Explorer, click on the drop down arrow to the left of All build definitions or All XAML definitions.
VS Team Services and TFS "15" RC2 and newer: Go to Build and click on the Security button in the upper right side.
You will then get a dialog like the following with the build permissions.