idea on making a princess crown ?

Answer 1

Cardboard, like the ones at Burger King, And sequins.
You could even get a Burger King crown and Paint it gold with spray paint first,and add some glitter while the paint is wet, then glue on the sequins or stick them in the wet paint as well.

Answer 2

If you're wanting to make a really fancy one use the metal and solder that they use for making stained glass windows. The metal can be bent and soldered into fancy designs then gemstones can be glued onto it.

One of my friends makes crowns in that fashion and they look just as nice as the ones you see in the pagents.