Hi,
Milling is overall weak in Legacy. It isn't unusual to face decks running
Emrakul, the Aeons Torn or stuff like that, that single-handedly invalidate your strategy.
If you want to build a mill deck anyway, I will recommend you to check some Epic Painter and Lantern Control decklists.
Epic Painter is built around the
Painter's Servant +
Grindstone combo, while Lantern Control relies on
Lantern of Insight,
Codex Shredder and
Ghoulcaller's Bell to put a soft lock on the opponent.
Moreover, if you're planning to stay mono-blue, you
must play the full set of
Force of Will.