This is the Blood Dragon Helmet from Mass Effect 2. I added some details to the front and a panel in the back that can come off so you can fit your head inside the helmet. I add locations in the helmet where magnets can be place to keep the back panel attached. They will fit D 8mm x H 3mm magnets.
This helmet is size for an adult make but check the dimensions in the pdf file. The units are in millimeters.