Alternativ "mirroring" of polygon primitives: 1) Select a primitive 2) Select scale tool (r) and move it inside out 3) Then you have roughly the same primitive facing the other way.
Changing the way an object "moves", when moving it by simply dragging the object around the scene. Press and hold Ctrl + klick one of the movement-icon-arrows Thus. klicking the up-arrow, you are able to move the object around in the x-y plane only, and keep the elevation when moving the object around.