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.

if you´re using the universal or high definition render pipeline you can just set the material property called "Render Face" to "Both" which will let the renderer know it should render BOTH sides of said material/mesh.

Like here:

If you are using the standard render pipeline you´d need a special shader for materials that need both sides of their surfaces rendererd like this one here: Free double sided shaders

OR, as stated by master1114, you´d need your mesh to actually have 3D surfaces. Meaning that each wall is not only single plane but two planes with a slight gap in between them where each plane´s normal is pointing outwards (: