Help with blender an materials!

help i have a castle that i made in blender and i have texture it but whit no suces so i exported the castle wall fbx file to unreal engine wiht no textures and i want to put the material manualy to it but its grey instead of rocks it turns from world grind material to stones but i see only light grey help how i can put my material manualy to my model please

make sure in blender you have created a uvw map for you mesh
you can find example videos on this on my youtube channel playlist Blender to UE4