Mostly that is a regional thing. Also not knowing what type of room your talking about its impossible to guess. Also the size and location of the room is another factor.

You could try calling your insurance agent since they deal in your area and as then for a "cost per square foot" rebuild. They should have the figures for you.

In most towns, where building codes exist, you can not convert a patio into a room, like part of the home.

The patio often does not have the footings you will need for walls and a room, and often you may have to actually dig part or all of it up to do your room.

Are you planning on doing all the labor ( or most) yourself, or hire it done, if hire, just call and get a few bids