Lots if greats word we idling builds but I haven't seen focused on the warhammer.
Use of a warhammer seems to go along with heavy armor, health and stamina. I know it won't block arrows and magic but you can use the warhammer as a shield and block with it and gain from the block perks.
But interestion realization that there doesn't seem to be any builds centered around the hammer. Maybe because its so slow and heavy.