You can use the terrain if you want to, it's okay. Also, back in these days i made the terrain with MCedit. What i would mostly do was place big squares and/or spheres and then retouch it with an air sphere, working my way down to smaller sphere sizes. This is quite an inefficient way of terraforming though, and MCedit is mostly for creating really big shapes/scenery where Voxelsniper could crash a server. Not sure what they changed about it in 6 months time, but so far Voxelsniper has proven alot more effective at terraforming for detailed scenery.