What to do if chimney bottom doesn't exactly match roof slope? In case of mill houses the chimneys have flat bottoms and roofs are sloped. I cut a hole in the roof and glue a piece of pink foam from the inside. After glue dries I cut pink foam to match the chimney and glue it in. Simple. No time consuming sanding and matching is involved.
I thought I was very close to finishing the project but then I found a bag with pieces for three outhouses. Mental note. Keep all parts in one place.