Big ones (balls) refers metaphorically to courage, force.
a. Usually in plural. A testicle.
b**.** plural (frequently as a mass nou*n). *fig. and in extended use.
(b) orig. U.S. Virility, (manly) power or strength; substance, force, vigour. Also: courage, determination. Cf. ballsy adj.
a1903 W. A. Henley in C. Harman R....
As earlier commenters have noted, the original "through the roof" idiom seems to have been "go through the roof," which Christine Ammer, The American Heritage Dictionary of Idioms, second edition (2012) defines as follows:
go through the roof 1. Also, hit the ceiling or roof. Lose one's temper, become very angry, as in Marge went through the roof when she ...