The Copenhagen Forum will host the next Green Day concert in Denmark on the 9th of October but the admission tickets are pretty much sold out... when I say "pretty" I mean that there are some tickets left... but those are around 230 euros. Furthermore, billetlugen.dk has unsold tickets on the waiting list... but you have a big chance to wait and not receive one because there are a lot of people on this list that want to go... and it's a matter of "stay in line" if you need a ticket. So it pretty much depends on how early you have subscribed for a reminder.
I would recommend the Green Day concert in Hamburg Germany... there are a lot of tickets left...