Question i would like to ask is a little harder tho:
What should those Ogres do? O_o
Having stuff like Ogres recognising AoE or hiding in a spot from which one can't target them from the roof would be solutions, but probably a complicated and not necessary one. I think the problem can be solved by two easier but more universaly useful solutions.
1) Better map design
Is impossible for Ogres to reach you if you stand on the roof? (I honestly don't know) If that is the case, then the map should be modified - there shouldn't be a place unreachable for a character. A longer path? Sure, but not a situation in which a player can tickle enemy to death from a safe distance. Naturally, if it is not in already, creatures attacked should go to the last spotted location of the attacked and perform a search for him - that should keep them away from stationary damaging AoE and make it a challenge for the attacker to remain hidden for too long.
2) Better system design
If, on the other hand, the Ogres have ranged attacks and are meant to use them to fight attackers on the higher ground - it's been argued before that like in 5e hide action should be full action. That way, the player cant hide and attack in the same turn with out spending extra resources, and at least putting some effort into abusing AI. Action economy exists for the reasons. This is one of the unforunate effects of making a dog's breakfast out of it for unknown reasons.
