That’s one cute robot cake!
It looks as though the sides of the cube that makes up the body are about three donuts across, I’m guessing that would be a cube cake about 8-9” to a side. So, yes, probably bake 2” deep sheet pans and then cut layers to size and stack them to the height that you need to make the cubes for the body and head. If you plan to make the body cube 8 or 9” tall, it will be best to put a cardboard square half way up the height of the cake, so that when you cut into it you’re only cutting pieces that are 4- 4.5 inches high.
For placing the head atop the body, the best bet is to use straws and cardboard squares for support, so that the head is resting on the cardboard and straws and not directly on the body. The tiny gap between the cakes gets covered with piping. The wedding cake section of the Cake Bible (or Rose’s Heavenly Cakes) gives formulas for cakes for different sized pans and complete instructions on how to stack with this method. Both books are worth having, but you can also check them out of most libraries.
If your Robot was quite small (i.e., you used mini donuts for the arms and legs, and the body cube measured maybe 4-5 inches to a side), you might be able to stack the head atop the body with just one straw going through both the head cube and the body cube to hold it in place (no cardboard).
For placing the entire robot atop a large sheet cake, I would use the same straws and cardboard stacking method for either a small or large robot, so it doesn’t sink into the sheet cake beneath it or shift or lean.
When I made a tiered cake using the straws and cardboard, I stacked the tiers in the place where the cake would be served so I didn’t have to move the stacked cake, and left the tiers in place for cutting the cake. Some people remove each tier before they serve it.
Good luck, hope you report back and post a pic!