Steam punk is a fusion of Victorian and futuristic designs. So anything futuristic, which is steam powered or heavily plated with lots of rivets would count.
The Rules and Regs
Build threads are a must.
Scratch building is allowed and probably necessary in most cases.
You can build Ships, Planes, AFV, Figures, Dioramas, etc, etc
And of course the most important rule?
A ribbon will be awarded at the end of the campaign for completion of a model, multiple entries are encouraged, but only one ribbon will be awarded.