With 11 Space Yard III Ships, you can build a sphereworld in 6 years (60 turns) -- #1 builds a sphereworld generator (5.5 years) and #2-#10 each build a cable starbase and a plate base (each takes 3 years).
Then you select the SWG base, then Stellar Manipulation, and then build the Sphereworld.
It's meant to be nontrivial in time and resources -- a Sphereworld starts at 150%/150%/150% w/ Optimal conditions, and your planet / atmosphere type, and can hold 200 facilities and a LOT of people.
It can also be PPP'd in a single turn.
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-- The thing that goes bump in the night