As long as there have been no roofline changes made to the USA Fit, Thule already has a kit for it. You will need either the Thule Rapid System or the Thule Traditional System. Rapid parts and numbers are: Gutterless Foot Pack (part #750), Bars - 120cm (part #761 for square, #861 for aero), Rapid Fitting Kit (part #1312).
Installation instructions can be found
Here