The Sonar extension uses the underlying ant task and passes parameters from buildr to ant. The parameters that you can use will be documented in the next release of Buildr. But to get you started here is a simple example that uses all the configuration parameters. The only property that must be set is "enabled", while the remainder attempt to have sensible defaults.
require 'buildr/sonar'
define "foo" do
project.version = "1.0.0"
define "bar" do ... end
sonar.enabled = true
sonar.project_name = 'Foo-Project'
sonar.key = 'foo:project'
sonar.jdbc_url = 'jdbc:jtds:sqlserver://example.org/SONAR;instance=MyInstance;SelectMethod=Cursor'
sonar.jdbc_driver_class_name = 'net.sourceforge.jtds.jdbc.Driver'
sonar.jdbc_username = 'sonar'
sonar.jdbc_password = 'secret'
sonar.host_url = 'http://127.0.0.1:9000'
sonar.sources << project('foo:bar')._(:source, :main, :java)
sonar.binaries << project('foo:bar').compile.target
sonar.libraries << project('foo:bar').compile.dependencies
end