Comment by ben_w

Mars… needs something rather bigger. I don't know what the most cost-effective solution would be, but Mars gets about half the per-area sunlight as Earth so it would need a reflector about the size of Mars to get the same overall insolation.

My guess is it's probably easier to make a bunch of greenhouses on the surface? But the scale is so huge that which is best will be affected by technology invented after you start.