The idea of these floating cloud cities in Venus's atmosphere came because despite the fact that Venus the hottest planet in the Solar System its atmosphere is considered potentially stable. This is because there is no air there and the conditions are almost perfect for creating small cloud cities. These cities would float naturally at about 50km above the planet's surface.
Also, researchers have found out that at that height, the atmospheric pressure and gravity is pretty similar to that of Earth. The temperature is also a pleasant at 75 degree Fahrenheit.