There are plenty of youtube tutorials on that, see e.g.

https://www.youtube.com/watch?v=JrpBmGCIiCQ

Muhammad Ismail,

You can't use Gaussian for building structures (that's for computational calculation purposes only). You have to use the builder tool of GaussView software. Here you can find a tutorial on how to use the builder tool by the Gaussian company itself,

https://www.youtube.com/watch?v=dqKWfXsEcWs

For the Materials Studio part, you have to use the sketch tool. I have made a tutorial on how to build any structure in materials studio (mainly, the tutorial is on how to build a 2D or 1D structure, but trust me, the nanocage thing will be easier).

https://www.youtube.com/watch?v=Xibd7IvL0Zo&t=18s

If you feel any difficulty, please contact me at www.aritraroy.live

Kind regards,

Aritra