My step son wanted a Halo and Xbox cake for his 8th birthday, so we Googled some images and tried it out. The Xbox was easy, just 2 9×13 cakes stacked and covered in fondant. Should have leveled it off but was in a hurry. I used a paint brush and food coloring to add the details.
The Master Chief helmet had to be iced, as my son does not like to eat fondant. I stacked and iced 3 8 inch round cakes, and topped them off with half a ball cake, shaved like the top of a helmet. The visor was just a piece of cardboard I cut out. For the visor I used a piece of fondant.
He loved it which is all that really matters.