I'm stuck on a part in Pokemon: Platinum, can someone help?

I'm in the part where Looker says he'll meet you in the Team Galactic Warehouse. I keep going in the warehouse, but Looker never shows up. Is there a certain room I need to meet him in? I can't get to any other rooms in the warehouse. Maybe I'm in the wrong building? If anyone knows how to get past this part, please help!