Ok. The heat and stretch method. The first thing I do is make the canopy "inside out" because you want to fill the inside with the clay or putty or whatever you decide to use. I use Sculpey clay, because you bake it when you form it into the shape you want and it will then keep that shape. You can get it at most hobby shops.
once you have your "buck" made attach it to something that can be easily held in a vice or by some other device. You will need both hands to do the stretching part.
Next you will need some "sheet" plastic. This can be the flat section of any "bubble type" packaging. in this cast I was able to "liberate" a piece
from the box of the Beard Trimmer I just bought. I use 4 pieces of 1/4" wood to hold the sides of the plastic to heat and stretch. I heat the plastic over a burner of the stove, and then stretch it over the buck held in the vice attached to the counter.
after it cools on the buck, take it off and trim the excess plastic and there you have it.