If you're trying to stabilize your star before it blows up in three years, I don't think you want to be building any more than is the bare minimum. Why build a city?
What might be more useful is a series of stellar objects between ringworlds and planet stabilizers.
If it is an emergency, throw up a stabilizer. If you have more time, you can build something more complex, expensive and more productive. But the bare-minimum, "save our butts" option should not have any frills
