Hey man.
I too am looking at a thrower alt when I retire him soon, with throwing lances also.
my thoughts were a 21/18 build(click to show/hide)
that would be my suggestion if you really want to use lances. If not go for less str and more Agi.
a personal favourite thrower build of mine is 15/21. But obviously you won't be able to use lances.Experiment with a few STF's and see what you like best(click to show/hide)