So after I beat Flobot I went to the rooftop garden for the first time and I saw Pichu being chased I wandered around up there for a while and didn't really know where to find him. I've since finished the main story and I've been up to the rooftop many times with no sign of him, so I'm wondering if he's somewhere else or it's weather based or if I just missed my chance by not finding him the first time. Any help would be awesome thanks.