From the attic the structure looks solid and is sloped to meet the roof line. Do I need to take it to level before a rebuild or can I add bricks to even it up. Do I need any type of lining?. How far above the roof line do I go?. Is a rain cover beneficial? Is this too big an undertaking. I have some masonry experience, some roofing experience, but I just like doing things myself. Not necessarily to save money but just the feeling of accomplishing something. But I am also one who can defer when something is over my head.
With a modest amt of experience in carpentry, roofing, and masonry, this is not too great a job to take on if it were at ground level but when performed off of staging at an elevation and location where you can get hurt and where the amt of physical work is doubled, it is probably best to hire it out. chimneys are re-topped here all of the time. weathering, poor old masonry, acids in the exhaust, and lack of maintanence tend to destroy them after eighty to a hundred years. Often, the interior will be in great shape still but it should be inspected by a pro to determine if it needs re-pointing or other repair before proceeding. A local pro can also tell you whether the solid rain cap is advisable for your area.