Alternate methods of establishing Rent are based on private sector models. They include, but are not limited to:
(a) Return on investment (ROI) approach or a similar cost recovery method used when market comparables are not available and/or GSA must ``build to suit'' to fulfill customer agency requirements; e.g., border stations; and
(b) Rent schedules for the right to use rooftops and other floor areas not suitable for workspace; e.g., antenna sites and signage.