[Baron Grazic]

In 1 PBW game I hosted, we started the game with a Ringworld in the very centre system, that was owned by a High Bonus AI.
The Ringworld changed hands a number of times, but whoever owned it was constantly building units attempting to hold it and it never reached its full potential.

I've never considered one in a PBW game, just to expensive and long to build, let alone hit the point where it would have paid for itself and be making a profit.