root object: invisible "terrain__h" piece. then a visible plane, the base plate u see. usually called "terrain" but can be named anything.
-- some piece of ur building
-- terminal probably?
and before u post a reply with it working but not fitting, make sure it's size is exactly multiples of 32. (so, extents of a 1x1 terrain square are: 16, 16, and -16, -16, assuming the origin is in the center.
also, congrats. I think that's the first textured model I've seen u make that doesn't have a texture that looks like you just covered it with a brick texture. Good job, it looks nice.