In my campaign, recently two players started laying plans to buy a part of land not too far away from city in hopes of building the base of operations for the team, or buy an already existing building for that. I know I can just go "Behold! The enclosed space, you can sleep here. Done.", but that seems bland and the idea of a building, maybe a small stronghold with some upgrades and all that seems very interesting to me. Alas, I do not know if I am as capable a GM as my players think, as I need to figure out everything from the ground up and be right on spot.
That's why I am asking if there are some sources on building/running/upgraiding/managing property/estate I could get my eyes on to get some ideas how to manage this. I am aware of some information presented in DMG about building a stronghold in downtime, and that's why I am asking about other ones, as I am going to completely disregard the existence of those from DMG, as they do not make any sense whatsoever, both in terms of cost, time and rules presented (if you do not oversee the building process personally, the time needed increases by 3 days for each day you are away, like, are your workers actively destroying it?), as well as not giving almost any useful information, save for some upkeep costs and staff, but no ideas for what is, or more importantly, what could be in there, how it could be used beside a warehouse, some overlay ideas, incorporating business, nothing.
I am planning on reading through the Kingmaker campaign book for Pathfinder to get some ideas, I heard it's quite good, but what about other sources? Are there even official ones for D&D? I would be glad for any ideas on the subject.