Geometric parameters of the concrete slabs

Hi Guys! I have the following question which is related to geometric parametrs of concrete slab. To make long story short I cannot extract the information such as slab’s Width and Length directly from the Revit model. I took a couple steps ahead toward my goal however don’t know what I am supposed to do next for getting those parameters.
Thank you!
Attached picture will give you an idea what I’m talking about