CMD + DRAG drags out a floor or ceiling from an existing perspective wall.
You can Paste a figure into the perspective and then use CMD + T to transform it and drag into the plane. Size correctly in one place, then when you drag through sides of the the perspective, it will alter to the correct size. You can drag around a corner as well.
Clone Stamping in Perspective
You can clone into a Perspective Grid and the perspective will change for you, so you can match things like floorboards from other floorboards in the image.
