This thing was made with Tinkercad. Edit it on-line https://www.tinkercad.com/things/3vJVt1qZRis
I located an .obj file of the scanner helmet. I discovered a web site to convert it into a .stl file, tinkered with it a bit: I made it a bit hollow and added what details I could with my Beginner abilities.
I do not anticipate anyone to completely download this helmet as is but if it could change, Add more details and chop it up for a 3D printer, it'd be a bonus.
A Scanner helmet from Halo 4