I don't have any of the codes, but 1/2" is the smallest size available off the shelf in A325, F1852, and A490.
There a lot of self tapping screws used in places where they were not supposed to be used. They make the self-tapping type of screws to 3/8" so you know someone has tried. I seen the larger sizes used on Purlins on some pretty large package buildings. I can’t remember seeing them on an engineered building with someone watching over the job. On thing that hurts using large sizes is the torque require to turn the larger fastener in steel unless you oversize the hole which lowers the strip out resistance.
This is from the supply end. You need someone from the structural side to bring you up to speed.