Use a chimney strap mount to hold a 10' pole for the antenna. Make sure that the antenna and coax is away from the chimney cap (where the smoke comes out) as far as is possible (either above or to the side).
Coax routing depends greatly on where you're scanner is (the shorter run, the better). It's easy to route through the attic bringing it in under the eves. Other options would be to run it down the chimney and through the wall near where the scanner is. Dont' forget to put in a small drip loop and seal the entry point to prevent water and insects from entering your home.
Make sure you properly ground the pole and coax!!! I can't stress this enough. Search this site and the web for good ideas on this topic. Again, make sure you properly ground the pole and coax!!! I always put a "lightning loop", a coil of several turns, between the coax ground/lightning arrestor and the entry point.