My costume has a helmet, a pauldron (for the shoulder) and a gauntlet. I an using plastazote to make them. First I needed to make cardboard mock-ups to get the patterns right.
Here is the front and and back of the helmet, with hindsight cello-tape would have worked better than masking tape.
To make the prototypes I basically made myself a nest of card, tape and armour books.
I need to figure out how to fasten the pauldron to my models shoulder, either D-rings and ribbon, or double sided body tape.
I didn't take a picture of the gauntlet before I dissembled it to take a pattern from, but there are lots of overlapping layers like there would be on a moveable gauntlet.