Roof geometry and construction is needed for both wind and seismic load generation. For wind load generation, roofs create wind surfaces that result in lateral loads, and for seismic load generation they contribute to the building mass.
Roofs are displayed in color in Roof Action if they are on the currently selected level, otherwise they appear in gray. They also appear in gray in Load Generate Action so that you can correlate the loads generated with the roof elements.
Roof Action becomes available for single story buildings when the Wall Action button is pressed and walls are created, or for multi-story buildings when the Extend Walls Upwards button is pressed. You must press on roof action before proceeding to create loads.