The Lord Hogwarts Challenge.
Have had this idea bouncing around my head for a while now. Not sure what year I would do it. Has so many possibilities no matter what year is decided. Haven't decided if I even want to take this on, but would love to see if anybody else wanted to. Just let me know.
Harry enters the Great Hall and as a joke, Harry stands on the Hogwarts Seal in the Great Hall and 'claims' Hogwarts. The result being that control of the Wards shift from Dumbledore to him and a new tower appears. Hogwarts is semi-sentient.
Harry assumes the title of Lord Hogwarts. Lord of Hogwarts, Hogsmeade and Protector of the Mystical Forest (Now called the Forbidden Forest). Only answerable to the Crown. Ancient Treaties come back into play.
As Head of 5 Most Noble and Most Ancient families, Harry must wed/betroth women to reestablish the family lines. (6 if Harry is Lord Black too).
Hermione is Lady Potter. Absolutely NO Ginny as a pairing. (my choice would be Daphne Greengrass, Luna Lovegood, Padma Patil, Susan Bones, and Su Li)
Ron/Ginny bashing is highly recommended, but not necessary.
If set before end of 5th year. As Lord Hogwarts, Harry offers sanctuary to Sirius.