I've found that free roam in the HP universe makes for the best role play, but I do have an idea if anybody is interested. It's a place that was made up in an old rp I did for awhile and I have a sub plot along with it that might appease both British and American alike.
Trebol Academy of Magic:
Trebol is a brand new school built on an island just off the coast of California. Muggles have no idea of it's existence and this is enhanced by a few protective spells. The island has beaches, and caverns. A small forest thicket to the Northwest of the school. Stables on the grounds and a ferry for students to use to get to the mainland on weekends.
The school is set under the American Ministry of Magic, but because it's new an assortment of students from all over the world currently make up it's population.
It's possible that an attack on Hogwarts has sent some of the students to the American school for their own protection. Hogwarts is known as the best in the world, and yet they find themselves in this new school off of American soil. You have the opportunity of going back to Hogwarts at some point. Maybe even play a little in both schools. It's a new setting to explore and set up as you wish. There's also possibility to roam freely outside of the school.
I'm not sure if you are still looking for ideas, but this is mine. I hope that it helps ^.^