MyDscConfig.ps1

Configuration MyDSCConfig {
    Node $ConfigurationData.AllNodes.nodename {

        if($Node.roles -contains 'MyRole') {
            # do stuff here, like calling DSC Resources
            MyCompositeResource StuffForMyRole {
                # ...
            }
        }

        if($Node.roles -contains 'MyOtherRole') {
            MyOtherResource OtherStuff {
                # ...
            }
        }
    }
}