When Games Workshop released Cities of Death, they released an Urban Basing Kit. This box set contains 2 pots of slate, 2 pots of resin details and 1 pot of razorwire that can be used to decorate the bases of your miniatures or cityfight buildings.
I managed to get one of the kits, which sadly was a limited edition and is now no longer available.
I first created a large 40mm round base.
I then tried a 60mm Dreadnought base.
Next I added modelling sand to change and vary the texture of the base. You will also notice that for the larger 60mm base at some point the barbed wire fell off!
The bases were given (as per my other bases) a base coat of Codex Grey.
The bases were drybrushed with lighter shades of grey and white.