Schengen tourist visa confusion [duplicate]

I am a permanent Resident of Canada and I am trying to understand the requirements of getting Schengen tourist visa.

I have not decided my exact dates of travel. I want to visit 6 to 7 countries. My appointment is with German Consulate for Schengen visa. All I know is I want to travel during the month of September or October for 2 weeks, depending on the best deal I get from travel agencies. How can I give them my itinerary or flight ticket details and accommodation details when I have still not decided on my exact dates?

I am also worried that, if I give hypothetical dates, they would issue a visa for just those 15 days and, later, if I cannot find any good deal for that period, it will be a waste.