Number of Casts: 4-5. Difficulty: Medium. I used quite a few casts from the previous building for this one, so if you're doing it from scratch, you'll probably need five casts, rather than four. As you build more buildings, you'll build a supply of spare blocks, which can be saved for later buildings. The Refinery was based the same as the Pump Station on an 8" sheet of MDF.
I decided to add a bit of color, as well as begin to hint at what the pipes might be carrying, in this case a strange glowing green liquid or gas. I also added some orange blocks on the side for color. They could represent either a ladder to get to the top of the refinery or lights on the side. On a design note, the Refinery is identical on the other side (hence the need for four casts--you need the pipe pieces). I'm thinking that symmetry might be another recurring theme.