Tip: If you only make one you don't have to struggle with making a symmetrical pair.
Start by cutting out the shapes you need in cardcoard. I wanted five layers and a ring going around my upper arm.
For the top layer and the ring around my arm I wanted more details. I glued on strips of foam mat in the pattern I wanted.
And then I covered all the cardboard pieces with faux leather. For the pieces with foam strips I was careful to glue down the fabric as close to the details as possible and making sure it stayed glued on.
For the edges I glued on a ribbon. Note: before you do this you should glue on another fabric on the backside of every piece, since you will see the underside from some angles and it is easier to glue that on before you attach the ribbons.
Then do a test assembly. All the pieces are held together with studs, also know as brads a reader was kind enough to tell me. I love it when you help me make the tutorials better, and when I get to learn what the materials actually is called.
Seen in use in the picture below.
The pauldron is attached with a faux leather strap going under the arm on the opposite side and fastened with a buckle in front.
On the backside the strap is only glued on. Use a dry brush and add some gold paint to highlight the details. For corners and edges that do not look perfect use studs or cardboard ornaments painted gold to cover up as you can see on the picture under.
Update: Here is a little more information about the studs I used. The larger ones are called furniture studs or upholstery nails, and can be bought at a hardware store, craft store or on ebay. I used pliers to bend the ends when punctures though the pauldron.
The smaller ones I am not 100% sure what is called, but I bought them at my local craft store Panduro in Norway.
Edit: I got information in a comments that the small ones are called "brads" - you learn something every day :)
I have also made a set of Skull Pauldrons for my Death Elf costume.