FSX How can I make "Physical" objects?

I want to know how to make a real "Physical" object for FSX, that is actually there and where the airctaft can go over and NOT trough.
I want to make a runway that way, so the aircraft actually rolls over it. Because if I use custom Ground Polygons, I have problems because the Runway partially disappears due to some smaller elevations.
I also need to make the terrain, as it's a little airfield and I would like to make like a little dirt apron and the runway next to it.
Thank you in advance!