spaceship size and fuel tanks

[Piper]

On a side note, It would be nice to have a list of common use items and list their specs for Addon Devs (eg LOX-200kg per 10L, Carbon Fibre 1kg/10m2 etc.)

Wikipedia has a really good chart of liquid rocket fuels, and gives their ratios, exhaust velocites, densities (which you need to find volume), and other specs: http://en.wikipedia.org/wiki/Liquid_rocket_propellants