Aluminium. Light blocks with a mass of 1 are the lightest. And what is there to protect your ship from? Purple missiles from those green jellies?
Well, for the eventual multiplayer this would be pretty important. Personally I think heavy redium for the front Medium/heavy Polonium for the sides, titanium for the back. Maximize protection in areas that are going to be hit alot, while keeping it relativity light. But this is for super battle cruisers anyways, so maybe im juts being stupid
Also, I had a Idea for modular ship design, instead of using custom made ships like we have know, we can figure out some "Modules" and just snap them together for quick ships. It would probably be ugly and pretty hard to make work but if we did we can churn out tons of good fast ships.
Some modules I was thinking about would be
1.Power generation, probably the center of any ship
2. Cockpits
3. Gun control
4. Guns
5. Engines, though they would probably not be there own module, but just slapped on where its best to put them
6. Storage
7. Crafting
These are the basic parts of a spaceship, and most ships wont need storage or crafting anyways. Guns would have to be custom made based on the position and which gun( Spinal cannons would need different rooms than anti personnel, etc) But figuring out a basic moduel for all of these would make ship building a lot easier and quicker for the multiplayer.
EDIT: Is there a way to take screenshots?