How to fill/show detected horizontal plane in ARKit-SceneKit using iOS 11?

I want to show user how far the floor has been detected in ARKit-Scenekit before allowing them to place any 3D object.

I want to fill the surface(floor) area detected by ARKit using some particles and let user place 3D object only in the surface area covered by particles and not anywhere else.

Is it doable? If so how to achieve this?