What are you talking about?
That's the way clouds look. The base of a cloud is flat.
The reason for this is, that is because clouds are formed, when vapor in the atmosphere condense. This process is depended on certain factors like temperature / altitude, air-pressure and water saturation of the air. Because of these physical factors, you will always see cloud bases as flat (since this is the altitude, that water vapor begins to condense) and the various cloud layers will always be at the same height. Depended on the composition of the atmosphere.