Hello, I am looking for an advice. I am doing a symetrical map in Kane's wrath worldbuilder. I know how to copy terrain. But is it possible to copy it with buildings and other objects? I think there must be a way, because for example when someone's doing a big symetrical city map, it must take a lot of time to complete it.

I don't know if you can copy them together, but you can copy them separately. After you are done with the terrain, select all objects you want to copy, hit ctrl+c and paste them (ctrl+v) wherever you like.