How would you say Borg ships are constructed in Star Trek? Are they built in shipyards like most ships or do they assimilate other ships that they come into contact with and just grow from there?
The foundation of Borg technology is nanotechnology. They have also incorporated the technologies of all the species they have conquered or encountered, which includes material synthesis.
I would think that the correct term would be ship-worlds, as all they would need is a resource world or two to consume in the process of creating their ships, with the occasional import of elements that they can't synthesize.
Reference Grey Goo as the basis for that hypothesis.