Assuming you're using
this Gamora and not
this incarnation...
It looks pretty simple, actually.
Two strips of fabric of appropriate lengths seem to form almost suspenders that connect to her pants and go underneath/behind the waistband.
Then everything is strewn between them. I'd use these parts to turn it form suspenders into a tank-top almost.
[EDIT] I'd sew in a mesh tube-top or something (am not a girl/do not know girl clothes) underneath the suspenders to from the main part.
