The ogres can throw chairs and whatnot at PC's on the roof. However, since it's turn based and there is no ready action, you can always end your turn in a spot they can't hit. Since Larian turned Hide into a Bonus Action for everyone, you can also end your turn Hiding for double safety cheese.
Two things should happen. Hide needs to be reverted to a full Action. That alone would fix all kinds of stealth cheese where you can attack and stay hidden, save for Rogues who should have it as a BA. Which would make Rogues.. rogues. But the AI should also investigate last known positions and sources of attack. Secondly, if they let PC's climb on a roof to pick off giants who can't get there, they need to make the roof destructible. Ogre smashes wall/beam/ceiling, PC falls down (Let's not forget DEX SAVE or Acrobatics check this time, ok?), takes heavy damage and is now prone at the Ogres' feet.
