Need help and advice

Hi guys !
Here the fact : I'm trying to build my own helmet (it doesn't exists any kit).

I built a solid base but I can't make a cast or mold because of my little flat ^^".
My question is : what can I use to make it wearable ?
I'd like you to tell me all the details I need for all the technics you can bring me, please

Here's a pic of what I have for the moment :


Thanks in advance guys !

I have some thoughts, but I need to know more to figure out where to go from here.
Can you be more specific to want you want to do? Do you want to make it more rounded and clean up the shape to it or?
Also, what have you done to this point, like what materials have you used to make what you have so far?

I want to make this helmet : Armure mandalorienne de Mandalore le Gardien - Star Wars HoloNet - www.starwars-holonet.com

I made the base with foam and cardboard. I put some fresh film around it in order to remove the finished helmet.
So my question is : what can I use (and how) to make the wearable part, knowing that I can't make a cast ?

Thanks for your answer dankenman