I can see waiting until mid-season if you are concerned about a #3 for the playoffs. There will be quality pitchers with expiring contracts on non-contenders that you can trade for. If we are dealing this offseason for another rotation piece, then I think a lefty under more than one season of control would be the target that I'd pay for in prospects or controllable position players. A transitional player to replace Gio after next year. Bring him in now, pushing Gio and Roark down to #4 and #5, strengthens the team for 2018 as a bonus.