I like your landscape ! Regarding the shadow of cloud I would suggest shading with a complementary color instead of black (here a red-purplish tone). Also keep the shadow shape simple to avoid being taken as form shadows and have hard edge. For composition, I would darken the background to keep the focus in the middle ground. Also beware of the road who lead the eyes away from the scene, you need to add a follow up that lead them back to the ruins. I hope it helps.
Thank you, noted! Should I use a normal layer for the cloud shadow ?
I am not an expert on layers. I would either use a multiply layer or a hard light or a normal with transparency. But search for better answers ^^

