You can use the "interface tool" in VNL to construct a supercell with graphene/MoS2.
Before you do the construction of graphene/MoS2 system and the related calculations, you may read the following paper:
Yandong Ma, Ying Dai, Meng Guo, Chengwang Niu and Baibiao Huang, Nanoscale, 2011,3, 3883-3887
http://pubs.rsc.org/en/content/articlelanding/2011/nr/c1nr10577a#!divAbstractGraphene adhesion on MoS2 monolayer: An ab initio study
Then you would find lots of hints: e.g., how large the sizes of graphene and MoS2 should be chosen to make the lattice be-matched.