Dealing with Existing Structures

Currently I model existing structures as a building pad and use a reduce element to stop other elements from cutting into my structure.
In order to move these structures between phases (of which I have a lot) I have to manually create the element and copy each outline into it (if i copy paste the reduce element it errors).

It may be easier to create a new element type for existing structures. It would be carried forward to the next phase unless it is demolished in the current phase (by another element).

An extension to this would be a really awesome tool I can use to see if I'm undermining existing structures / pipes that will require expensive shoring to maintain. As you are identifying not only the outline of the existing structure, but the elevations.