Oops sorry, it is UE4 , not UDK.
Yeah , regarding extracting building from google earth, there are two ways :
3d ripper
3dVia printscreen.
But I am not getting into that argument , as the quality I am receiving is very low , and hence I am no longer using those buildings. I have found out a better solution.
You can see the street view of almost every corner of San francisco in Google earth, so you can see the buildings from really close up. So it is good idea to observe the buildings from every angle , and design them from scratch in Maya/3ds max.