I got frustrated trying to saw a notch in some plastic HO scale chimneys, so I decided to make my own.
I started with the working drawings from the Great Northern Historical Society's Modelers' Pages (#392, "Section Houses and Facilities.")
I'd already enlarged the image to use as a template for making walls and roofs, so I just scanned my enlargement at 100% as a starting point. I opened The Gimp, and used one of Clever Models' excellent brick textures to make a simple box with a notch on the bottom. I used that scan of the enlargement to get the size and shape of the chimney correct. I inkjet printed the result on matte photo cardstock, along with a partial sheet of just the brick texture. I cut and assembled the chimneys, adding strips of heavy black cardstock to the interior as I folded, to give it a little thickness. I touched up the edges with gouache paint as I went along. I cut two strips from the brick texture -- one strip was three bricks wide, the other, one brick wide -- and I wrapped them around the chimneys near the top.
The first chimney must have taken about 45 minutes to make, and I messed it up badly and threw it out. By the time I'd made three, they all looked uniformly nice and my time dropped to about 15 minutes for each.
Here is one of the chimneys test-fitted to the roof I completed earlier.
I opted to scratch-build these four models for my client rather than buy and assemble four GNHS kits, since it's actually a savings for him -- cutting the pieces myself and assembling them takes only slightly more time than merely assembling a kit. This also means the money I would have spent on the kits -- which are about $25 each -- goes directly in my pocket. Another advantage to me is: I only charge the client for the time spent on the buildings I make for him, and I track my time very carefully, so as I go along, I can make a fifth model on my own time and at my own expense, and sell it to another client later.