When tracing rooms the software will automatically create the exposed roof surfaces in your rooms.
This means that for flat roofs no additional Roof sections need be traced, and no roof Setup is required.
While tracing rooms the software will automatically create the rooms external roof surfaces:
Any parts of these surfaces that then have rooms subsequently added overhead will be automatically changed to internal ceilings, as long as the adjacent rooms are within your Adjacent Tolerance range.
This means that for buildings with flat roofs, and no rooflights, no additional Roof tracing or Setup is required.
For more complex roofs - eg sloped or pitched roofs with rooflights - the Roofs module can be used to trace roof sections and Setup these over rooms below. Guidance on roof tracing options can be found in this article.