Go and find the map called "The Ultimate Terraining Map 3.0", it has a lot of premade models and all ingame models (by that I mean doodads and destructibles, NOT units), changed so it's faster to find, what you are looking for.
And also you should get World Editor Unlimited for RPG terraining, if you don't have that, then you're almost certainly gonna get stuck because of the doodad limit in the normal WE.
hope this helped