That is a fairly tough question to answer without any specifics as to the size of the rooms you're planning to add, the type of flooring you want, any special windows or skylights, as well as if exterior walls would need to be removed, any landscaping removed where you want to add the rooms, etc.
I would talk to and interview 2 or 3 local builders or contractors to give you estimates as to what you would like to do and then check their references and go from there. They would probably want a plan drawn up of the room additions to be able to give you estimates of the cost to put them on the home.
Good luck with your room addition.
Prudential Prime Properties