Screenshots in Unreal 3 :
I made a simple setup with one directional sunlight casting realtime shadows and a large specular point. No lightmaps were baked. The sky is a simple dome with a gradient texture.

Initial concept:
I modelled a simple basemesh to get an idea how i could build up the model with modular shapes and repeating textures, then did a paintover until I felt I had enough information to start working on the final model.

Construction:
I modelled a base with parts that can easily be moved around for quick modifications. I also created several add-on meshes to add to the base, they can be moved around, instanced and LOD steps could be added for performance. I also used vertexcolors to get more ambient shadows on the mesh to better bring out the shapes.

Texture flats:
Normal maps are partly rendered and partly painted by hand. The model uses one 1024*1024 for the base and another 1024*1024 for the add-on meshes. The specular maps were kept pretty simple, i think they serve their purpose in this case.