After that using a round soft brush with opacity set to 40% the shape and other dynamics checked i add some dark clouds all there where i want to have a dark image.
Once i had enough dark clouds i start to add some lighter one over them and also try to bring some orange colour in there tho have the same colour like in the other elements of the composition. This sky don't have to look really natural just to give the natural feeling of a sky and of light coming from the right direction so it don't matter if is to blurry or the cloud shapes are not to clear.
I keep working on the same way using the same brush just changing the size until i get a sky that I am satisfied with. You could try to paint you one one or you can use the one i made for the next step
Step 9:
Open thesky.jpg from the source folder or use yours and drag it into the main image over the background layer name it sky. Select the texture layer above and set the blending mode to Soft light. Then select the scratch layer and do the same but also set the opacity to 65%. Go back to the texture layer and make a copy of it the drag the copy at the top above all other layer Set the blending mode to soft light and the opacity to 65%. Now make a copy of the sky layer and Set the blending mode to multiply then click on the 2nd icon at the bottom to add a layer mask to the sky copy layer. Select the gradient tool (G) and use a linear black and white gradient. Select the mask and drag from up right to down left to cover up the light part of the sky copy layer like in the image below.
