Any better material that would allow my custom shape? (Schematic in another comment, and I’m going to add it to the post)

End unit of a townhouse style condo. Should I not bury it at all? But I’d still have to level out the ground because of the slope? Shorten its life by how long? Does that change at all if I’m looking at plywood? I’m aware of the prep and substrates, I just wanted the dirt as the top layer before the stones to support the moss. Or am I that much better off using some kind of square shape and dropping the moss idea?