I never built any Sphere or Ring World, for lack of the need to do so. (Well, in a regular game that is, I tried once to check how it was done)
Incidentally, I fail to see a reason why you would want to build a Sphere World. These require a *lot* of research points compared to Ring Worlds, and they require twice as much resources and build time than a Ring World. Besides, you would need fifty turns to outproduce a non-breathable ring world, and one hundred turns to have more facilities than a breathable ring world. So many turns are needed for this Sphere World to be more profitable than a Ring World.
So is there any reason why you would want to build a Sphere World, unless if you do happen to have few stars at your disposal? I admit I fail to see why you would want these. (Apart from trying to build the fabled Sphere World boasting 240 Cultural Centers. That is what I call a very strong planet indeed.
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