How to remove sections of cube?

hello, so i want to make a wall with windows and a door, i know it would be easier to make them from separate objects to make the shape, but to make it lass laggy i would prefer less game objects, what i was thinking was somthing like how UDK does? where you place an object that looks like what you want inside the objects and then it deletes that section? is this possible in unity?

No.

This is modeling. You need to do it inside a modeling package such as 3DMax, Maya, Sketchup, Blender or Cheetah3D

Actually, yes.

It’s not the best way though, you’re better off doing that in modeling program as Jeff stated, but check out GameDraw, which allows you modeling something above primitives inside of Unity.