Regarding three-dimensional (3D) topological insulators and semimetals as a stack of constituent 2D topological (or sometimes non-topological) layers is a useful viewpoint. Primarily, concrete theoretical models of the paradigmatic 3D topological phases such as Weyl semimetal (WSM), strong and weak topological insulators (STI/WTI), and Chern insulator (CI), are often constructed in that way. Secondarily, fabrication of the corresponding 3D topological material is also done in the same spirit; epitaxial growth technique is employed, making the resulting sample in the form of a thin film. Here, in this paper we calculate $mathbb{Z}$- and $mathbb{Z}_2$-indices and study evolution of the topological properties of such thin films of 3D topological systems, making also a comparative study of CI- vs. TI-type models belonging to different symmetry classes in this respect. Through this comparative study we suggest that WSM is to CI as STI is to WTI. Finally, to test the robustness of our scenario against disorder and relevance to experiments we have also studied numerically the two-terminal conductance of the system using transfer matrix method.
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