Before we actually begin working on the model, let's make clear the difference between a regular spacecraft and a steampunk spacecraft. Although both of them are based on science fiction, the steampunk spacecraft has a few important characteristics that differ from a regular hi-tech spacecraft.
Imagine a world where the advances of science and machinery were actually developed centuries ago. For example, imagine medieval knights using hi-tech armor and destroying castles with rockets. It may sound strange, as the rockets have been made only for the army in the last century. What would a fighter jet look like in the Middle Ages? It would be a mix of steel, glass, and wood.
The steampunk environment is made out of these kinds of things, modern objects and vehicles produced and developed in a parallel universe, where those discoveries were made long ago.
The secret of designing a good steampunk vehicle or object is to mix the recent technology with the materials and methods...