Things you for sure want to include:
I know it may seem a little overused, but rain and lightning, to me, is a very intriguing idea. I think there's a lot you can do with it and it can make for a very good story. Rain is something every good quidditch player and team should be able to cope with and leran to fight against. I don't want to work with some random, totally illogical force of nature being inflicted on the quidditch pitch, such as a volcano or a tornado. I want to make this, for the most part, believable.
Things you would rather not include:
As stated before, I don't want to include anyhting illogical, random, or just completely unbelievable. (i.e. lets please not have a hurricane go over the pitch!) Also, I'ed rather not include any canon characters in this i.e. having Harry be the seeker for the Gryffindor team if that's who we play. I think it adds a more personal, unbiased touch if we use our own characters. Plus, we would be able to create our characters and the game however we would like without being tied down by the actual descriptions of certain players and their personalities, if that makes much sense. (If not just tell me)
Where should this take place? (World Cup, Hogwarts, Weasleys' back yard...):
I think it would be good to have it at Hogwarts. It's a bigger atmosphere to work with. Plus the added pressure of school rivalries, peer pressure, the cup, and winning for you're house. It seems that there would be more at stake, a bigger, driving force for the players to strive to win.
Not much, we can just get started and see where it takes us.