I made one a few years back, it works a treat.
I bought some titanium foil, cut it to height, folded the two edges so they can clip together to form a ring, it unclipped to go inside the pot. Once I'd done that I used a hole punch to make perforations one the bottom so it could breath.
A bit later I made 4 holes at the top so I could use tent pegs to hold the pot.
Photo attached (sorry about the size, posting from mobile). You can see the modified pegs at the top right, the cross stand I had as backup in case I didn't like the tent peg design.
Shield weighs about 14g, 6g for the modified pegs. I use an Evernew burner (45g I think), nothing else comes close without being much much heavier.
Everything fits in my Toaks 550ml pot with the (also MYOG) stuff sack to hold it all together.
Quick FYI (on the off chance you don't know) some parks only allow gas fires.