Initial thought
Clouds are in all sizes and shapes. We often like to imagine what a piece of cloud looks like. Sometimes, the shape of high thunderstorm cloud looks like it could easily host a castle. So what about a real castle? A real white castle on top of a piece of cloud. It brings the rain and no one can see it from ground. Who lives in there? I am not sure. Maybe some weather management spirits.
Digital concept
The castle matches the bottom of the cloud. Imagine half of the castle in shadow and the other half bathed in sunlight. It is not pure white but more of a warmth white. The blue lights behind all the gates and windows indicate that there are some activities in this castle on clouds.
The vast land feels empty, the background sky feels blurry. Therefore, the castle can become the focal point.
Summary
Every time I paint cloud it feels different. To me, there is no one SOP that suits cloud. It changes all the time as its nature.
I thought about Jack and beanstalk after I finished this one. A concept of a castle on a cloud is always tempting.