Outside custom story - Need help and hints

[Brute]

You will need to work with planes, that's for sure. You can design the terrain with it, that would be the solution for beginners. But if you want something professional, you can create terrain objects in a 3D Model Software. The rest shouldn't been a problem. You can use the Amnesia models or use planes for creating buildings, statues... etc...
The last thing would be the sky. I remember seeing a tutorial about it in the forum, but don't ask me where.
Good Luck, my friend!