You have modelled a roof in Archicad, and you want to cut a hole in in its geometry. When you use the Roof tool to draw the shape of the opening, you end up creating additional roof planes instead of a hole.
Solution
Let's go through the steps:
1. Select the existing Roof.
2. Make sure the Roof tool is Active.
3. Draw inside the boundary of the selected roof. This will now become a hole.
TIP: How to remove a hole from a roof