Geoffrey Landis made some interesting proposals about floating habitats on Venus:
Landis has proposed aerostat habitats followed by floating cities, based on the concept that breathable air (21:79 oxygen/nitrogen mixture) is a lifting gas in the dense carbon dioxide atmosphere, with over 60% of the lifting power that helium has on Earth.[5] In effect, a balloon full of human-breathable air would sustain itself and extra weight (such as a colony) in midair. At an altitude of 50 kilometres (31 mi) above Venerian surface, the environment is the most Earth-like in the Solar System – a pressure of approximately 1000 hPa and temperatures in the 0 to 50 °C (273 to 323 K; 32 to 122 °F) range. Protection against cosmic radiation would be provided by the atmosphere above, with shielding mass equivalent to Earth's.[6]
At the top of the clouds the wind speed on Venus reaches up to 95 m/s (340 km/h; 210 mph), circling the planet approximately every four Earth days in a phenomenon known as "super-rotation".[7] Colonies floating in this region could therefore have a much shorter day length by remaining untethered to the ground and moving with the atmosphere, compared to the usual 243 Earth days it takes for the planet to rotate. Allowing a colony to move freely would also reduce structural stress from the wind.
At this moment in time there's no way to even practically get to the surface in anything other than small scale. It would be easier to build habitats at the bottom of the deepest oceans of Earth.
If there was the technology I suppose you could rig a big enough solar shield to screen the sun from Venus and put it into permanent darkness; I suppose eventually the planet would cool enough for the Co2 to freeze. If you could then chop it up - literally mine it - and take it off planet someplace else, then you might be able to do something with what was left. But that technology is at least 500 hundred of years away and such a process would likely take a thousand years in any case.
