I constructed the dome ring in the same manner as the base ring.  I initially laid up the ring inverted on the table.  I lined the inside of the splash/centering guard with aluminum flashing.  I fastened 3 2-inch diameter furniture glide pads equidistant around the base ring splash/guide guard.  When the dome ring is inverted and placed over the base ring, these glides will act as bearing points against the flashing and keep the dome centered.  The bottom photo is of the dome ring assembled and riding on the base ring.  The cutouts on the top of the dome ring are attachment points for the dome ribs.  The dome ring and base ring were constructed to give the dome a diameter of 7.5 feet.