Please could you clarify your question? A nanosheet is no longer a crystal, meaning that no Bravais lattice can be assigned to it. So, what do you then mean by "they should be converted to their natural lattice type". Also the shape of nanosheets is not uniquely defined. One may choose some shape related to a particular experimental sample or propose a nanosheet with some unique properties, hoping that it can be realized in real-life experiment. So, it is pretty much your choice.