Activate the Scale tool and choose Use Selection Center in the main toolbar. Then scale down the selected 3 vertices. This is not important, rather just to give the pool an interesting shape.
Now leave the Vertex sub-object mode. Then restore all the 4 viewports and Zoom Extents all to see the NGon in all viewports. Activate the Move tool. Then in the perspective viewport, click on any axis of the NGon while pressing SHIFT key. Clone Options dialogue box will appear. Set Number of copies as 3 (make sure "Copy" option is selected in the Object group). Then click OK.
Now you have 4 NGons in total. We should rename the NGons for better handling them. So, click Select by Name button in the main tolbar. In the Select Object dialogue box, highlight NGon01 and then click Select.
