Calculating Figures for Raising Up a Roof

[Nicole Romano]

I am in the Hudson Valley of NY. I am wondering if anyone can give me some ball park figures on "blowing the roof off" of a house. The house currently has more or less a Cape Style 2nd floor with dormers. There are side knee walls, but they are only about 4ft. This eats into the usable square footage bc you literally cannot walk the entire upstairs. You will bonk your head on the ceiling. I want to raise the roof. The house will be taller bc those knee walls will be 8ft instead of 4ft. How do I calculate this? And if I want to add a bathroom, what should I calculate to plumb that? Thanks in advance.