Are you planning to let them free-range daily?
If not, you'll want a large enclosed run attached to the coop. Usually for turkeys, it's at least 5-6 feet high (chickens don't need that much height).
If you do free-range, be warned that heritage turkeys will roam fairly far away (and return at night). You can always fence them in, but they fly also. So you must either cover your coop, or clip one wing (flight feathers only) to prevent flying (every 3-4 weeks).
Also, keep in mind that your coop must be predator proof (from dogs, foxes, raccoons, etc.). I learned the hard way when I lost a number of my turks to foxes. They had been roosting in the meadow for 6 months before the foxes discovered them. I hadn't thought foxes existed in my area.