Above is a screenshot of my reskinable chimney object. It can
be retextured so that it matches whatever building it is put on top of.
Because it's an object, you don't have to Optimize when you create it, and it
affects cell count and (depending on the Properties) the pathfinding database a
lot less than a chimney made out of terrain brushes.
Without scaling, the object is 13 units high It also has a vhot so you can easily attach a particle effect (i.e. smoke).
Click Here to download the model.