Design phase 6
This phase counter the problem of detecting clashes when there are more than 1 primary elements in the project, in this case was the wall. when there were more than 1 wall in the Revit space, the Tool.IntersectionChecker was not able to perform as how I want it. It would select every wall instead of selecting the on intersected clash wall.
However the new Element.IntersectsElements nodes enables me to solve these problems.