I turn my stool seats slightly concave on top for greater comfort.  The legs are thru-mortised, wedged, and epoxied into the seat.  This makes the joint extremely durable.  Stools can be made of almost any North American or tropical hardwood and to any combination of seat diameter and height, as long as the spread on the legs is adequate for stability.  They can be designed and sized for a particular place in your home or a particular use.  For example, one of my stools had a rectangular saddle-shaped seat and was sold to a musician who found it perfect for playing the cello. 

 The display pedestals can used to position an indoor flower pot at the right height to catch the sun's rays near a window, to display a sculpture, or to hold a candle  They also show what can be done for the base of a table.