Can we demolish a small part of existing slab.
(We can divide the slab in two parts and demolish one part. But then we will see another lines in existing phase).
We can hide those lines in existing floor plan.
But is there a better way to do it.
I shall post an update on new solution for this problem.
Since We say that Revit is like "Virtual Construction", It should behave like real life (We should be able to demolish a part of existing floor).
Though I am o.k. with the current arrangement (using linework tool).