Missing a lot of faces

Hi everyone,

I've been trying to import my model from CityEngine, SketchUp, and Blender into Unity and my model is missing a lot of faces.

I reviewed some similar topics on this forum and tried the solutions suggested by others (I tried to recalculate normal in Blender, and increase the size of mesh in Unity) but none works.

I created the model in CityEngine (Esri) and exported it to Unity (I tried obj., fxb., and dae.) but most of the faces are missing. I originally thought maybe it was related to CityEngine but it turns out I can open the model files on Blender/SketchUp and the faces are still there. So I think it is a Unity problem.

I am wondering if it has anything to do with the size of the model? Right now my model has more than 10,000 normal/vertices.

Can someone tell me what I should do? It is kinda urgent. Thanks.