I really like the idea of hiring the NPC and then having them follow you to where you want to build (whilst remaining within the faction territory).
Definitely require high alignment and I also wonder how easier it would be to incorporate having to provide materials to assist with the building either using the quest hand in system or a chest marked with an item frame.
Would be great if the structures were not insta-spawned though I imagine having it appear over time would require additional coding and possibly be even more resource intensive...
Also if it is possible for the original post to be reassigned to me I'm happy to expand on the idea with the suggestions posted in this thread.
I like the idea of an specific NPC though that would be more work. I was thinking the captain would be the most logicial of the pre existing NPCs
BTW - I'm the original poster though I didn't think to create an account first.