I started making helmets with pepakura, which is a software where you print out the pieces of the helmet on card stock and then cut them out and fold and glue multiple pieces together till the whole helmet is formed, and after all that is the post process of needing to harden and smooth out the helmets.
Pros - its a cheap way to make a nice detailed helmet, all you need is
Pepakura (a free software)
A printer that prints paper
(And if you want to go the extra mile of hardening it then you would need some additional stuff)
Cons - it is very time consuming, it can take me more than a week to finish the forming and putting the helmet together if i'm spending at least 2-3 hours on it everyday.
Cutting out the pieces can be very tiring
Some pieces are so small that sometimes when trying to attach it to another piece it does not work due to the density of the glue
It is a very messy and time consuming project
Conclusion - I think it would be a great place to start if your into cosplaying or making your own armor. As you can see from my pictures though I have never gotten farther than partially hardening the helmet just due to how time consuming it is and not having as much free time as I would like. Nonetheless it is a satisfying feeling when you finish putting the helmet together knowing it was done with merely your hands and dedication.
Side note: As you can see in the picture I own Simplify3D, and that is because a while ago I used to own a 3D printer CR-10S5, I had also bought over $900+ worth of files from Do3D (Clone Trooper Armor, Commander Cody Helmet, Iron Man Mark L Full body, War Machine Mark 2, Mandalorian Beskar Steel Armor, Venom, etc.) I was looking forward to be able to print all these but for almost a year of owning the printer I was unable to print anything successfully due to the printer continually glitching: filament constantly jamming, the bed becoming un-leveled in the middle of a print, whatever else you could think of that could go wrong. It was very disappointing but I eventually I sent it back in for a refund, my plan was to buy another one but around the time my refund came in my parents were having a hard time with money so I had lent that money to them.
More than anything I would love a 3D printer that would able to print all the wonderful files I have bought from Do3D