I am in the process of purchasing an older home Circa 1890. The upstairs has a sloped ceiling. I would like to increase the head room to make it easier to get furniture and things up there by adding a shed dormer. The problem is, there is no ridge beam on the existing roof. All dormer plans seem to include the use of an existing ridge beam. Infact, the rafters are not even dimensional lumber. They are logs. How do you add a dormer this this type of situation?