Download MeshBrush FREE Unity.
MeshBrush is a Unity editor extension that allows you to paint meshes onto your GameObject’s surfaces.
Quickly detail and enhance the overall look of your scenes by directly painting your prefab meshes onto your GameObjects.
You can define multiple meshes to paint, how to randomly scale, rotate or offset them, and eventually change their size additively upon generation, without the need to actually modify any of the original prefabs.
Add multiple MeshBrush script instances to your GameObject to define several sets of meshes you want to paint, and adjust the randomness parameters for each set individually. MeshBrush will then cycle through your sets randomly and paint the meshes you defined based on the parameters of the corresponding script instance.