Episode 5 stuck on roof

I am currently on episode 5 on my I phone 5. I went to the roof of the building on grove st 1 to talk to blitz and teeter and now the door to go downstairs is locked and there's nothing I can do on the roof. It's asking me to scavenge 6 crates of scrap metal but I can't exit the roof because of the door being locked when I click it it says complete more quests to unlock but how can I do that when I'm stuck on the roof? Please help!!!