I'm a professional scenic artist, and found your messages while looking up info on flooring. Before you do anything, you have to decide how realistic you want these clouds to look, and then go spend some time looking at real clouds.
If you just want big cartoony clouds, paint the wall sky blue, and make the clouds solid white, big and round, maybe even somewhat recognisable shapes (dog cat mouse etc.)
For more realism, start with the sky blue again, then go at the clouds with a big soft brush and white, light cream and pale grey paint. when you paint the clouds think lightest on top (white), dimmer in the body (cream) and a little of the grey underneath it all. I would even suggest creating the whole cloud in light cream first, then add the white and grey before the cream dries.
Also, use glaze with your cloud colours, use 50% glaze, 50% paint, and add a tiny bit of water. Make sure they are all the same finish (flat, glossy etc.) Using glaze allows some blue to show through, and means you don't have to get the cloud perfect from the start. You can come back to it after it dries and tweek it.