Tenant Wants To Build Screen Room. Let Her?

My tenant is about to move in and she already talked about building a screenroom ON HER DIME. She knows that the screenroom will be mine when it is finished. There is also a clause in my lease that says I need to give written permission before such alterations/improvements are done.

I think it will add value to the house. Is there anything I need to watch out for? Do I need to approve of the contractor who will do that? Any advice will be helpful.