When making your custom brush, you will need to derive a black and white image of your cloud to make your custom brush, so try to find an image that will translate well to grayscale and open this image in Photoshop., This is one of several ways to quickly change your image from color to grayscale, and can be found under the "Image" heading on the menu bar. Under "Image," select "Desaturate" to convert your image.Windows users can make use of the hotkeys: Ctrl+⇧ Shift+U

Mac users can utilize the hotkeys: ⌘ Cmd+⇧ Shift+U


, Using the selection tool, chose a sample from your cloud image that you would like your brush to imitate. Be sure to limit your brush size to a maximum of 2500x2500 pixels, as this is the largest brush size., Now that you have your brush sample in black and white and selected, click on "Edit" from the top menu bar and then choose "Define Brush Preset." This will prompt a dialogue box asking you to name your new brush.
 You can quickly open Brush Settings by pressing the F5 key. Opacity and size can be adjusted in brush settings, and these can give the illusion of variety to even repetitive brush patterns.
Find a clear picture of clouds, or take one yourself.
Turn black and white with the "Desaturate" feature.
Select your brush sample.
Set your brush.
Adjust settings as necessary.
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