Some parts of the object are invisible from one angle but visible from another angle. Is there any solution?

It looks like the walls oft your building are made out of two dimensional meshes. A mesh consists of a lot of different triangles. However, only the "front side" of each triangle will be rendered. If you for example create a rectangular 2D mesh, you will be able to see it from one side but not from the other side. So it is not possible to create a simple mesh that can be seen from both sides. There are a lot of similar problems posted (e.g. https://stackoverflow.com/questions/39374811/unity-mesh-triangles-flipped).

I suggest you use some three dimensional objects to create the building walls.