I will be working on a unique project. It a museum that is underground. The entrance is at grade. It will kind of be like entering a cave. How do I make a surface for something like that? We will need earthworks also. I guess my proposed surface would be the ground floor of the building but not sure how to Civil3D the ceiling for earthworks.
Civil 3D will not model a tunnel. You would need to create a surface for the ceiling and a separate surface for the floor. Beware of vertical or overhanging faces as Civil 3D does not support that functionality.