I recently built a tower with a hip roof on it. I was reasonably pleased with the way the roof turned out but realized that I had forgotten to include a smoke jack in it. So I took my trusty Xacto knife and went to work boring a hole in the roofing material where I wanted the roof to be. That was simple enough. But the hard part came when I tried to get the smokejack to stand straight up in the roof. No matter what I tried, it wanted to lean one way or another. While I realized that this "could" be the way that many of them were, it wasn't what I wanted so I went to work, thinking about a way to resolve this.
Here's my solution: Since the smokejack was only going to be a piece of round plastic shaft, I cut a piece of it about four inches long. On one end, I quickly filed down a point that would easily go into some scrap foam insulation board I had laying around. Next, I used a square to line up the shaft material then pushed it into the foam so that it was perpendicular. I carefully placed the roof over the shaft and added a few drops of plastic cement. After letting this sit for a few hours, I gently & carefully removed the shaft & the roof together as one properly aligned piece. I added a little scrap plastic on the inside of the roof for additional bracing, trimmed both the inside and outside to length, painted the visible part black and I was done. Where's my Easy Button??!?