Start by crafting 4 Metal Dinosaur Gateways and Large Bear Trap. Place 3 Metal Dinosaur Gateways in an open square formation, but don't connect them, leave small spaces in the corners. Place a large bear trap in the center, and lure the Giga into it. You'll have seven seconds to run around and place the fourth Dinosaur Gateway. Now the Giga is pinned in the square, use whatever method of applying torpor you like, but I highly recommend using your best Crossbow, arrows are cheaper and a better investment than darts.
I dare you to raise one!! They are savage if you got two high lvl parents (about lvl 140ish) and you get imprinting on it. The thing will become an adult with about 230% melee and basically one chomp any bronto!!! But on the down side you loose your job and your girlfriend
When taming a giga you want to use 4 gates with a large bear trap. Set down three of the gates in a U shape and shoot the giga from far to aggro it and lead it inside of the trap. Once the bear trap holds the giga in place you have 10 seconds to run and place the fourth gate behind it. I highly recommend taking a throwaway bird, when taming gigas a lot can go wrong.
Make 4 metal dino gates and 1 large bear trap. Place three frames and door into an incomplete square and the large bear trap in the I between them. Lure the Giga into the trap and while its trapped place 4th down to make the square. Then just light it up with tranqs