Do horizontal stabilizer of ga planes e.g cessna 172(or ultralights e.g lazair) have cambered airfoils inverted to provide the tail downward force or do they have symmetrical airfoils at negative aoi to provide the downward tailforce during flight.
Generally they are either symmetrical airfoils (like NACA 0012) or flat plates (especially on fabric airplanes). The horizontal tail doesn't have to work as hard, or operate over as wide an AOA range, as the main wing in generating downforce, so you can get away with what amounts to, on most fabric airplanes, a slightly streamlined sheet of plywood.
There are some specialty exceptions. The Zenith 701 family of homebuilt STOL aircraft are unusual in having a heavily cambered flat bottom airfoil for the tail (actually, flat topped, since it lifts downward and is installed "upside down"). They did this to get as much down force as possible at very low speed and since the airplane is a bit of a slug anyway, the draggy tail airfoil wasn't so much of a penalty.
A homebuilt I had started on but never got anywhere with, called the Pegazair, had something similar, having ripped off a few of the 701's design elements.
Also, it was a practice at DeHavilland Canada to use tail airfoils with a bit of negative camber to improve down force at low speed on their STOL designs. I'm sure there are others.