The "rent" depends upon the terms of the deal. Who is doing the construction? Who is responsible for the costs of construction? If you are merely leasing the land to this person and allowing him to build on it, then you would receive less rent than if you were to do the build yourself. Will the tenant have the option to purchase the property? If so, they should compensate you additionally for this right. Similarly, if they are given the right of first refusal to purchase, that too deserves additional compensation.
Dunkin Donuts is a huge national franchisor. They must first bless the location before they will allow someone to negotiate for its use. Check to see if DD has signed off on the location before you get ahead of yourself.