You could do them with the blobs technique (recommended); paint a blob of color and then shape it till you get what you want, to then proceed and outline it. Or you could try sketching lines like pencil and paper, but it may take you a while to clean them up after you get the shapes down.
It would be really awkward.. To have copyright infrigements on art techniques.
Imagine, having to pay some random artist 10 bucks to use dithering, or paying Jackson Poll0ck a million dollars in order to drop paint buckets on the floor.
My cloud style is somewhat simple to make, once you get used to it. It took me a few tries to get it right myself.
If you're going to make it yourself, then.. First goes the cloud shape in the darkest color, then the darker shades, and lastly the bright areas on the tops. Brush tool, middle circle; then refine it with the x1 dot, AA, and it's done.