To erase part of a building: Hold ⌥ ALT and draw. The selected area will be removed.
Hold ALT to draw an area to remove
The area has been removed
EDITING POINTS
You can edit points of the drawn shape by clicking on the Edit Points button. When you move a point, the entire building updates accordingly.
To move a point, click on any point of the wall and drag it where you want.
To add a point, click anywhere on a wall.
To remove a point, hover over it and hit DELETE or BACKSPACE.
To delete a segment, click on Edit Points, hover between two points, and press DELETE or BACKSPACE.
To exit that mode, click on one of the shapes above the button.
CORNERS
You can also choose to toggle the Bevel Corners button at the very bottom to have soft or sharp angles to your walls.
USEFUL INFO
📌 Good to know 📌
You can’t mix different wall types within one building using this tool.
You can’t edit the floor or the walls from the Wall or the Pattern Shape tools.
To disable the wall shadow, you need to select the wall in the Selection Tool and disable the shadow from there.
The floor is designed to have some randomness in it, and will change everytime you update the building.
Walls from the Building Tool interact with cave walls from the Cave Tool but walls from the Wall Tool don't.
Author's Thoughts
While the Building Tool is powerful to make quick and dirty maps, it doesn't allow much control.
If you plan on spending more than 10 minutes on a map, then I'd advise you to use the Wall Tool and the Pattern Shape Tool instead.