In some cases complex shapes (specially in slopping roofs outline blocks) must be modeled.

 

For example if a part of a slopping roof must be removed the cut tool can be used to implement this. See below a common case:

 

 

 

 

When the cut tool is cliked the user must draw the cut lines.

 

 

Finishing the action the roof block is divided into two blocks based on the cut lines.

 

 

Then you can remove the undesired roof block by deleting it. The result is shown below: