Raising upstairs roof

[Robin Maciejewski]

My grandmother recently passed. She. Owned a home with 2 huge bedrooms upstairs that have slanted celings because of the roof being very steep. We would love to buy her house from my mom but those upstairs rooms are not functional the way they are. They are otherwise very large rooms and there's a lot of attic space up there. What would the cost and process be to get rid of the slopes or at least make them less prominent by raising the roof 3 or 4 feet. As it is a dresser barely fits against the wall because the slant is so low.