He smiled when she was up there with him, and made sure she was standing steady before taking the blanket from her. He didn't unfold it all the way, leaving just enough room for them to sit together, before laying it down on a part of the roof that wasn't as steep as the rest. Then he pulled out his wand and murmured a few spells to inflate the space under the blanket and give them a more comfortable surface.
"It's not the best view of the city," he said with a shrug, putting his wand back and moving over to stand behind her, placing his hands gently on her hips to keep her steady. "But it's a good view of the stars."