It's not a step by step guide but here's a look at my warlock helmet in progress.
I drew the shapes and patterns of each panel that i could see on the design. Then i cut them out of eva foam and used the heat gun to form the curves needed.
I then used hot glue and impact adhesive to bond the foam together.
I used a pair of ladies tights stretched over a circular piece of eva foam to create a screen to look through.
Step 1: Internal Padding
Next i added foam padding inside using hot glue to make it a more comfortable fit.
Step 2: Adding Detail
I have added the side panels onto the helmet and have used the dremell tool to smooth out the edges.
Step 3: More Detail
Just a pic showing some detail. To add cut detail, first cut the pattern u want with a sharp knife and then heat with a heat gun .(pic 2 )
Step 4: Pva Glue Seal and Paint