Making the building's roof landable?

Hi
I am working on this building that has a helicopter ramp, what do I need to do in order to make the roof landable in fs2002 (I don't want anyone to sink into my building.... it might cause some damage). I am using gMax.
thanx
Liran Bar, Israel
I am working on this building that has a helicopter ramp, what do I need to do in order to make the roof landable in fs2002 (I don't want anyone to sink into my building.... it might cause some damage). I am using gMax.
thanx
Liran Bar, Israel