Nice idea, pity it’s no longer available…
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.
The rear view.