but rather than having designated stats and roles, they'll be empty hulls of varying masses with perhaps a few key properties.
This I really like

Your ships have various properties and it's up to you to balance the equipment on board.
- All equipabble objects (engines / weapons / scanners / etc) have a class number; power requirement; and occupy a certain amount of "space"
- All ship types have "space" that can accept ranges of equipment depending upon the class
- All equipment requires power that is derived from the engines, allowing you to overfill your ship and switch things off and on when required
- Whatever is remaining on your ship you can designate for real cargo space
Then it's up to you what you do with it:
- Type 1 "combat class" ships:
---Mark I - III engines
---Mark I - IV combat weapons
---Mark I life support
---Mark I - II scientific equipment (scanners and the such)
---20 units of space
---cost $1million credits
- Type 2 "combat class" ships:
---Mark I - V engines
---Mark I - VII weapons
---Mark I - II life support
---Mark I - II scientific equipment (scanners and the such)
---35 units of space
---cost $15 million credits.
Haulers, scientific vessels and transport ships could be similar accepting larger engines but lower weaponry; better support for scientific equipment and have more life support areas; larger cargo space and obviously cost considerably more. And so on.
Yes - I really do like the idea of total choice - aka modular ship building.