I just want to confirm my understanding of your circumstances. So, you’re looking to place buildings in Unity at specific points on the globe, and clamp them to the ground. I’m not sure if you have put these buildings into one Cesium3DTileset, or if they’re separate – could you clarify?
In the meantime, I will mention that Cesium for Unity includes the ability to “anchor” a Unity object to a specific location on the globe. This is possible through the CesiumGlobeAnchor component. With a globe anchor, you can specify the lon / lat, as well as the height above the WGS84 ellipsoid, that an object should be. So if your buildings are all separate models, you can attach a globe anchor to each one.
Getting an object to automatically clamp to terrain is a bit trickier. We have typically instructed our users to raycast to the terrain, then move the objects to that point of intersection, like in this thread.
I hope that helps. Let me know if I’ve misunderstood your post, or if you have any follow-up questions or concerns.