The sign for "giant" will depend on what you are talking about.
If you mean "giant" as in a fairy tale type or giant, then you can
exaggerate the sign for TALL by using a bigger movement, eye-gaze,
and a more intense facial expression (or even the mouth movement
that looks like you are saying "CHA!"
This sign is particularly good to use for describing people but not
good for describing buildings. This version of TALL means "very
tall" and if you were telling a fairy tale of some kind this sign in
context would mean "giant."
You can do this sign with less facial expression and not so high up
and without the upward eye-gaze to mean just "tall" rather than
very-TALL (basketball player height or "giant")
If you mean "giant" as in
"big" see: BIG
You can learn
American Sign Language (ASL) online at American Sign Language University ™
ASL resources by Lifeprint.com © Dr. William Vicars