(or Why did I build large terrain pieces?)
The basecoat was the same Blue spray-paint-can color that my previous fortifications were colored with. I chose to do the whole structure, inside and out so that I could achieve the blue-drybrushed-with-Grey effect wherever I needed to in the structure. Obviously a lot of the interior details will be painted in something different than the "custom ferro-crete color" I'm using.
After that I applied a craft paint Copper to the Aquila and important building details.