The phrase "a giant one" is correct and usable in written English.
It can be used to refer to a large object or entity, often in a comparative context.
Example: "I found a giant one at the store that I couldn't resist buying."
Alternatives: "a huge one" or "a massive one".
Mr. Pulte was part of a postwar generation of builders who turned a mom-and-pop industry into a giant one traded on the New York Stock Exchange.
You could simply build a hutch, but try to go one step (a giant one) further, and give the little rascal a true habitat.
The part of the descent sequence that worked well for Schiaparelli differs from the rover and will rely on four parachutes, including a giant one 35 metres in diameter, instead of just one.
I saw a giant one growing in a 7-Eleven parking lot in Pennsylvania on an oak tree that weighed 12 pounds.
And a big wardrobe is a must – actually, you need a giant one!
We have lost a giant, one of the greatest figures in contemporary Africa.
It feels like I have to do a giant one-way circle around the town before zeroing in on my destination.
Indeed he is like a giant, one-stringed string instrument.
Cee-Lo Green appeared here (Saturday and Sunday, ITV1) as a giant one-man Chelsea Flower Show.
It has put small wind turbines atop the lamp posts in some of its store parking lots, and it has installed a giant one-megawatt wind turbine at a distribution center in Red Bluff, Calif.
The overwhelmingly positive tone of the meeting — the majority leader, Senator Harry Reid of Nevada, called it a "love-fest" — suggested that Mr. Obama was enjoying some success in pushing the centerpiece of his agenda: a giant one-two punch of tax cuts and government spending intended to jolt the moribund economy back to life.
