Again this is difficult to answer as you are providing much to work with — which system (monolayers) do you want to create? Do they have the same unit cell parameters and so on…

Anyway, my recommendation would be to turn to ASE (Atomistic Simulation Environment) that could help in creating two instances of the monolayers structures and then couple them. Clearly, you need to provide some pieces of information like the inter layer distances and the relative atomic displacements. You would get in principle a large number of potential structures and you need to select some of them that make more sense (for example because you found them in the literature).

The hard way, would be to (some of these steps would be necessary in any case)

1) Study how commensurate the unit cells are. How many repetitions of the cell of one of the two materials you need to consider to match a cell constructed by many repetitions of the second? These usually correspond to the two integer numbers whose ratio best approximates the ratio of the lattice constants.

2) Once you have these, you need to create the supercells. There are some tools available for this task, some can take a QE input as a starting point.

3) You merge the two set of atomic positions into a single input file, with one set shifted upward with respect to the other. Also you add the lattice parameters of the supercell obtained in 1). Create the appropriate list of atoms with their pseudopotentials. And you are essentially done.

4) You might need to study if sliding of one of the monolayers with respect to the other produces a minimal energy.

I hope this helps,

Roberto

Use burai package

For building monolayers, hetero bilayers, etc., you can use software named 'vesta' and there are many tutorials available in YouTube on this, whichyou may check. And then, another software 'burai' may help you to generate input files for different dft calculations(e.g-geometry optimization, scf, band structure calculation etc.) corresponding to the structure that you will make in 'vesta' before. Also, many tutorials available in YouTube on 'burai'. Hope, those may help.