To make the crown, I used litho plate, but you could use craft aluminium, sprayed with Brass Enamel Spray Paint. To fit over my wig, I made it 60cm long and at the top point of the crown, 10cm high. The necklace is 2.3cm at the narrowist point and 4cm wide for the point.
Two small holes were drilled into the necklace and a gold chain attached with jump rings. The wig is from Etsy, member ID littlepennylane. All details about the wig are in the video.