@Kevin L. Sharp,
What about pvc toilet flanges?
They are almost 1/2″ thick, which would be too high if placed on top of the finished floor.
The metal ring flanges are only 1/4″ thick which works out great.
I hear so many conflicting opinions on toilet flange heights, but most plumbers say to set the toilet flange flush with the finished floor, or up to a 1/4″ above it.