[Nodachi]

Baron Munchausen pointed out:

I would like to see colonization changed, though. It should not be possible to live undomed on a non-native planet type. Gas giant planets aren't suddenly good environments for surface-dwelling creatures just because they have been altered to different gases. Gas-native races are 'flyers' or 'floaters' of various types, remember. So your colonies on non-native type worlds should be domed regardless of the atmosphere. Your race will always require special structures to live there.

With all due respect Baron, this is not completely accurate.

We'll assume a rock native population for this.

You have a domed colony on an ice world and your atmosphere converter just finished its job. You may now disassemble your dome, because you don't need it to hold in your atmosphere, and spread out. Of course your buildings must be heated but now you can put them anywhere you want.
Real World Example: Antarctica
Sci-Fi Example: Hoth

Now the fun one!
You have a domed colony on (should be in) a gas giant. How would this even be possible? Bubbles. A "domed" colony would be nothing more than an airtight bubble floating in the atmosphere. How does it float? Just like a ship in water. The higher atmospheric pressure of the planet would hold it up (we won't discuss keeping it in place ). Now your atmosphere converter has been working its little heart out and manages to convert the atmosphere. You can now build pylons on top of your bubbles tall enough to put platforms up where the pressure is more comfortable. With enough bubbles and platforms you get more usable space. If anything you should get more facility slots on a gas giant even if it's "domed" and tons more after the atmosphere has been converted. How many Earths would fit in Jupiter?
Real World Example: Yeah, right!
Sci-Fi Example: Bio of a Space Tyrant series by Piers Anthony

It all comes down to being able to use the space more efficiently. I'm not saying that all the physics involved are correct, but hey, this is science-fiction. I'm also not saying that the game should be changed to reflect these ideas, that would destroy game balance.