I had to replace the bonnet/poppet assembly on our sprinkler system's backflow preventer (a Febco 765) this year and the new piece didn't come with a canopy. Rather than pay $25 for a curved piece of metal, I opted to just make my own.

I decided not to include screw holes in the model because different backflow preventers have different configurations. I printed this one in PLA because I'm curious how long it will hold up outside, but materials like PETG and ASA are generally more recommended for outdoor applications.