Carpenters: What is the approximate cost of adding a dormer to a cape cod home?

I have a 3 bedroom cape and there are two bedrooms upstairs. One has a slanted roof and I would like to raise this. What is the cost of this? Also, what is the cost of adding another room to the house? I'm thinking of a guestroom. What is the cost of extending my small dining room another 6 feet or so outside the house, which would mean tearing down a wall to make it more square? I'll appreictae any carpenter help as well as anyone who has had this done. Thanks!!