turrets

Depending on what figures you buy, you may find you have lots of spare guns that you can use to adorn your terrain. Then again, you may not. There will be other occasions when you need something a bit different, and lots of terrain model makers create their own from bits of wire and tube and other small parts:
This example was created by Tuco.

1. the end of a ballpoint pen.
2. from the Warhammer siege defense box (out of production) but could be easily scratch-built or salvaged from a toy.
3. a cut-up piece of sprue, the ammo belt comes from a Tamiya accessories pack.
4. an old Lego part
5. another old Lego part
6. 6x lengths of tiny brass tube glued around a slightly longer plastic rod. I think the thin transparent plastic tube that contains ink in ballpoint pens should work as well.
7. another cut-up Lego part.
8. what's left of the bars that framed the barrels, it was made from sprue but it proved too fragile.

The gun to the right was made by Kishkumen and sits on top of a 1:24 scale remote control car (so it's a big bigger than our normal wargaming scales but could easily be scaled down).
Six lengths of narrow tubing were glued around a central shaft of the same diameter. They were cemented at one end and the other end they were spread apart a bit (to create that taper toward the muzzle that Gatling guns have) and then cemented to the wide tube.
The little details on the gun are just bits of strip styrene glued to the outside. For instance, the ammo belt is connecting into an I-beam. The ammo belt is a corrugated bit of sheet styrene with two strips glued to it and then bent into position.
The little camera is a short length of square tubing with the ends closed off and a tube glued to the end. A bead was stuck in to make the lens and short bits of strip styrene make the handle and eyepiece. It's supposed to be an old VHS camera stuck to the turret and connected to a TV monitor so the driver can aim the gun.
The gun was painted with enamels and then given drybrush with silver. I have to repaint it frequently. The car often tips over and scrapes the gun, exposing plastic.
The guns on the fortress to the right were made by bugbait_nz using Game Workshop (trapezoid shaped) plastic sprue, cut down milk bottle tops, plasticard, cotton bud plastic tubes, carbon fibre arrow shafts, bike spokes and paper.
The bodies of the Autocannons (the larger guns) are made from nine pieces of GW sprue, glued in threes to make 'sheets' which were then glued on top of each other to make a block; which was then shaped. Cotton bud tubes were used to make the ammo and glued to a carbon fibre shaft. Plain photocopy paper wrapped was around some more cotton bud tubes forms the barrels, with a bike spoke for the recoil rod and also used to hold the barrel on. The spoke wire can be bent and makes lining up the barrel easy. The green plastic pieces were cut from bread bag ties.
The Lascannons are mostly made from GW sprue, with 1.5mm thick plasticard on each side and top, barrels are plain paper rolled and glued around a cotton bud tube, with more rolled paper to make the dangerous end of the barrel and filed at an angle. Cardboard was used to make the two small rings that go around the barrel with copper wire being used for the coils.