If you enclosed a patio and then put a roof over it;
I would guess that most Apprisers and Assessors would not consider it part of the squarefootage.
If you added on to the house, with slab foundation, plumbing, electrical, roof, and windows; I would guess that most would accept it.
It may be a good-news/bad-news thing;
You can say that your house is now 1200 squarefeet larger and worth more, but the Country will have a reason to increase your assessment.
Good luck and may God bless