Get Floor Outline and interesecting floors with geometries

Hi there, and first of all, I wish you a very happy new year 2018 !!

Well, here is my question : I’m trying to get the outline of a floor, I mean, to get the curve so I can use it in dynamo. My goal is to cut an existing floor with a geometry (a cylinder for example), so I can have, in the end, 2 floors.

Do you guys have any ideas?