Okay so after examining it I decided that Trebol just didn't fit... so I found something else that I thought worked much better.

[hider=Salem School][URL=http://s191.photobucket.com/user/Dori623/media/Salem_zpse54334ee.jpg.html][IMG]http://i191.photobucket.com/albums/z307/Dori623/Salem_zpse54334ee.jpg[/IMG][/URL][/hider]
This is an actual building out of salem with a bit of imagination I can see it being quite expansive. Also it's just off the water front and I was thinking that when people walked past it they could see a broken down old ruin of a building that seems impossible to break into. They also seem to lose all interest in the building the second they wander up to it xD

And basic layout:
School Layout:

Main Building -

1st Floor - Lobby, Banquet Hall, Caretaker’s office, staircases, elevator shaft
2nd Floor - Nurse’s ward and office, History of Magic classroom
3rd Floor - Headmaster/mistress office, Transfiguration classroom, Arithmancy Classroom, Muggle Studies classroom
4th floor - Charms classroom, potions classroom
Roof - Herbology Greenhouse

2nd Building - Student Housing

1st floor Main Lobby - Lounge/Common room, Prefect Dorm
1st and 2nd Floor West Wing - Wisteria 1st - 3rd year
1st and 2nd floor East Wing - Gladium 1st - 3rd year
3rd and 4th floor West Wing - Foxglove 1st - 3rd year
3rd and 4th floor East Wing - Viserious 1st - 3rd year

3rd Building - Student Housing

1st floor Main Lobby, Lounge/Common room, Prefect Dorm
1st Floor East Wing - Veserious 6th - 7th year
2nd Floor West Wing - Wisteria 4th - 5th year 
2nd Floor East Wing - Gladium 4th - 5th year
3rd Floor West Wing Foxglove 4th - 5th year
3rd Floor East Wing Veserious 4th - 5th year
4th Floor West Wing - Wisteria 6th - 7th year
4th Floor East Wing - Gladium 6th - 7th year
Northern Tower - Foxglove 6th - 7th year

4th Building - Bell Tower

1st Floor - Defense Against the Dark Arts classroom
2nd Floor - Ancient Runes Classroom, Divination classroom
Bell Tower - Astronomy

Grounds -

The Quidditch Pitch
Stables for Care of Magical Creatures Class
Docks