You draw a small room (space enclosed by walls), then place a doorway that you make into an "arch" by way of the doorways "Arch" tab in the Door Specification dialog for the doorway. to finish off you would add the pedestals using custom slabs that you apply a white material.  To get the thickness shown in your photo you might use a custom thickened wall to get just the look you need and want.                                                                                                                                                                          DJP