Thanks for the feedback, those cockroaches come flying from outside through my balcony which is common in summer season anywhere you go in Sydney. The fly at night attracted to light. My balcony is quite open to the landscape. That's why you found big cockoaroches as they come from outside not from the inside of the apartments. If II had seen baby ones or small ones then I would definitively worry about having a nest in my unit but I don't. They come from the streets flying. My guest back in July didn't have hay problem because it was winter time. Thanks for the comment