I am trying to reproduce this rooftop, but I have some trouble.
I tried with a "clouds" texture to create the random dirt, but it looks more like waves in the ocean.
I tried with a more dirty ground, like the one I found here :
I tried to recreate the dirt myself, it looks good only when it is one image. But once it is in Blender, the texture is repeated and it gives a bad repeated effect. So I tried another version with light gray and blue, and the map effect, so that we don't see the borders, but it is too simple :
Would you have some tips for me? The texture will be large enough to fill the size of the rooftop, and the view will be close to the ground, so I must add some details as if we were close to the ground.