1. You can not, at least not without implementing a rather powerfull streamed terrain system.
What you can do thought is dynamically modifying the terrain to let it look like it is infinite / very large and move the building in the opposite x-z direction than the ship and keep the ship above the center of that terrain all the time
2. Calculate the height at the position. TerrainY on a regular terrain
What you can do thought is dynamically modifying the terrain to let it look like it is infinite / very large and move the building in the opposite x-z direction than the ship and keep the ship above the center of that terrain all the time
2. Calculate the height at the position. TerrainY on a regular terrain