better strength makes larger muscles (notably the upper legs, the torso, and the arms)
endurance removes fat. it should be impossible for the player to become fat without mods, but npcs with endurance less than 25 should get noticably porkier- 1 endurance is morbidly obese
agility increases the size of some muscles and removes fat.
speed changes the size of lower leg muscles slightly, and removes a tiny bit of fat
if i have the details wrong please dont dismiss the idea on a whole
willpower,luck and personality do nothing. skills should do nothing too. and being a saint/ an ass should do nothing .
secondly, races need base body types. the idea of buff elves is stupid. most races should be able to have a choice. a light build should make the player small and at max attributes look have a build like bruce lee , a heavy build means at max attributes more muscle is present and the player looks more like a rugby player/boxer. light, medium and heavy builds should exist that are playable. light builds should give a bonus to endurance and agility (not sure about endurance, because in game it means how much damage you can take rather than making movement easier)and a penalty to strengh and health- whilst big builds have a bonus of strength and health. medium build should be neutral.
the player should be able to control some aspects of their body, like hips, neck,hands, how veins show up, boobs,tattoos,body hair etc.
oh- and spell effects like damage strength or fortify endurance shouldn't morph the body. do note that npcs would have more freedom, bethesda might decide to throw in super fat argonians with full stats