How do I attach a new pitched roof to my existing roof ? What data do i need to even need to begin to plan this out? How do I determine the pitch of the existing roof so as to match the new roof addition to the same slope? Area to cover is 15 x 15 , single story house. I want the eve/edge of the new roof to match up with the eve/edge of the existing roof. The house is 20yrs old if that makes any difference. The cover will be open , no walls.