Roof — with a generator

If your building already has a roof, this won't show you much. Draw a box (or a few) with nothing on top first, then come back here.

Set those boxes to Room for a more realistic result — select them, then change Building Role under General in the right panel.

Press Rectangle (or just type rect in the command line) and place it where the roof belongs.

With it selected, open Details in the right panel → + Add Generator → Roof Profile Generator

Select the rooms below — they must be Box or Extrusion — and turn on Fill to Neighbor in the Geometry section.

The roof is still editable. Select it, open Details again and change Slope Angle, Eave Length and the rest — it rebuilds as you type.