Has anyone worked out a uniform way of constructing the Hopf algebra of a Chevalley group out of the root system (or, more precisely out of the root datum for reductive groups).

By "uniform", I mean a method that works for any type, not case by case.

If yes, can anyone point out a reference in the literature? Ideally, I'd like to see the construction over the integers, but I'd still be interested in constructions over a field.