5. And Voila you have a new surface, now simply extrude this surface
and rotate it so the top view has the square!
6. Now using a similar tech to earlier, select the same two inner vertices in the drag them down just slightly, and move in and do the next two and then the remaining one. T
his should give you the shape you have been after
I'd be very keen to see if this work for you so be sure to show me your results!
Good Luck
Steve