When it comes to constructing large scale structures, especially starships, you need to really think about how you would go about construction.

In a world I'm building as a hobby a civilization of mine uses massive, genetically engineered plants to construct starships and bases.

In the case of a starship, a "seed" is dropped on a remote location, usually an uninhabited moon or asteroid. An orbiting ship goes into a geosynchronous orbit and beams a high energy laser over the "seed" location. The plant has been genetically engineered to conduct this energy very well. This enormous energy causes the seed's metabolism to skyrocket and spring into action. The plant starts building the starship by transmuting surrounding material. The plant then bears "fruit": the starship, which then launches into orbit. These particular ships in my world are propelled by magnetic fields and monopoles.