Please do not complain about errors just download the materials in the description and everything should be fine.
Download them and then extract the into your garry's mod folder :P
This here is my rooftops 10 map, I've updated it to be prettier and polished.
-Fixed the skybox
-Added a new type of ending to the map
-Replaced stalkers with combine guards
-Made buildings better, bigger, stronger
yet again you might need these materials:
Beta textures: Valvedev.info
Old textures: Hl2-beta.ru
Don't forget to also move the models in to your Garry's mod folder.