Perhaps 'flying above the roof' would have been more accurate than 'on the roof', but seeing as how they're 12 stories up and you were on the ground, there were bound to be some depth perception issues.
Besides, you would have missed anyway-and you can still hit him with a regular attack, I won't require a move action, I'll just require that you be able to make a move action.
It's fine, at fifteen feet, I can see how he might not have been able to tell given the distance. Just now he's been asked to fight not 1 but 2 flying opponents. If he had been able to tell, he would have corrected Stunner and attacked someone not flying, like Tempus, Cannon, or the rock guy with the gold.