@Anssi I just watched the link the OP shared. The problem is that you are not drawing your rectangle in the same context as the wall you are trying to edit. Doule click into the group with the wall and acutally draw the rectangle on that face.
After a while of thinking about it, I made 5 identical rectangles WITHOUT any offsets. I had no trouble at all removing the rectangular space. Then I selected the perimeter and made my offset. I Pulled them up to make frames and added in some green glass.
each group, each component is like a world of its own.
When you draw stuff at the beginning, you draw them in the context of the whole file. easy.
Once you’ve made a group, you have two contextes available : inside the group, or anywhere else.
To draw inside the group (and modify it), you must first double click on it. If you don’t, well you’re drawing in the general file.
What Aaron meant by context is that. In the screenshot you gave, we see your rectangles as thick lines. They are profiles. It tells us that you didn’t enter the group before drawing the rectangles.
Therefore, you have a group containing a roof on one side, and a few rectangles on the other one. they can’t interact, they are in a different context
Groups/components are airtight. meaning that unless you first enter them (2 clicks), nothing you’ll draw will actually impact them.
It’s a common mistake that most of us here do now and then. you exit the group without noticing, or you forget to enter it, and you end up drawing on top of it.