Dear Kowk-Long Lee,
There’s no limitation for the number of lattices (“site families”) of the sites of Builder objects (i. e. systems or leads). What you want to achieve should be perfectly possible. Let us know if there are any problems.
Instead of using four stacked 2-d square lattices you could also consider using a single cubic lattice. This would be simpler for example in the case where the hopping integrals between neighboring layers are the same in your model.
Christoph