Building and Maintaining a Domain
The Pathfinder adventure path Kingmaker includes a relatively short and simple system to control and expand a territory that is ruled by PCs. These rules, along with rules for battles between armies, are going to be reprinted in the Ultimate Campaign book that will be released at the end of this month, and will then be put in the Pathfinder SRD for easy open access. However, the rules themselves are already open content since the release of Kingmaker, so replicating some of them here is not an issue in any way.
Now the Ancient Lands are not intended as a setting for campaigns of conquest or politics, but PC are expected by default to belong to one of the countless small clans that have staked out their small territories and have to defend them from outside threads and also make sure they won't be devastated by famines, monster infestations, or rebellions by challengers to the chiefs rule. Even if the PCs don't rule over the clan themselves, the Kingdom building rules might still be useful for GMs to see how the clan is doing and what happens in battles between armies, in which the PCs are only a few warriors among many. For this reason, I want to see how the rules can be adapted and what you are thinking about it. In any way, it would always be a completely optional element to games set in the Ancient Lands.
Domain Building
Not every chief or warrior who has a handful of followers behind them would be called a king, and in the Ancient Lands, that title is reserved for the most powerful rulers who have the loyalty of several major clans behind them. As such, I will instead use the term Domains, which is more general and generic enough to represent almost any territory. Also, not every major settlement is a city, as that term is used in the Ancient Lands for less than a dozen places that are almost legendary in wealth and power. Instead, the rules for building and running cities are simply refering to Town.
A village is any cluster of farms, but might also be a logging or mining camp. In the Domain Building rules, they are not tracked individually. The amount of villages and what people live and work there is not really relevant. Either a region is producing resources, or it is not. (More on that later.) A town is a commercial center where the people from the villages come to sell their food to the townsfolk and in turn buy all the things they can not make themselves at home. All the specialized craftsmen and merchants in a domain are assumed to be living in the towns and this also is where all the governing takes place.
Domains are based on a Hex-map. Every hex represents an area about 12 miles across. A hex can be either wilderness, farmland, or a town. A chief can lay claim to a wilderness hex, but that it pretty much meaningless until it is inhabited by people loyal to the chief and his warriors patrol the area. Again, the number of farms and villages is not relevant here. Also, it doesn't matter what kind of resources the area produces, it is simply counted as income for the domains treasury. There can of course also be farms and villages in the same hex where a town is, but for simplicity they are not counted towards resource generation and income.
There are rules for annexing a hex and converting it from wilderness to farmland, but I won't go into those here as they don't really matter right now. You can look them up when they are in the PRD.
Now the real meat of the Domain Building rules are the towns. Again, for simplicity, the normal homes of the townspeople that make up the majority of the town are not tracked. All that matters is the special buildings, like specialized craftsmen, temples, castles, and so on. At the end of every month, all the farmland hexes plus some buildings in the towns are generating income, but a great deal of it will also be consumed by the people living in the domain. But if you have a surplus in income, it is added to the treasury in the form of Build Points. You can spend these BP to increase your farmland by expanding it into new wilderness hexes or by creating new special buildings. This might include actually building new constructions like a castle or temple, but could also represent making special arrangements to get an alchemist to settle in your domain. Like offering tax breaks, providing infrastructure, giving bribes, and so on.

While you don't actually build a new house with your own money and pay for the training of the alchemist, it still puts a dent in your resources.
Following is a list of special buildings you can build in any of your towns. If you conquer a town it obviously comes with already existing buildings. You might also decide to turn a small irrelevant village that the PCs have visted on their journeys into a town. In that case you could have the town already start with certain buildings for free, like a witch the PCs had dealing with earlier.
Town Stats:
Alchemist (18 BP; must be adjacent to 1 house): The laboratory and home of a creator of potions, poisons, and alchemical items.
Town base value +1,000 gp; 1 minor item; Economy +1.
Barracks (12 BP): A small building where additional warriors in the chiefs service are stationed to defend the town together with the townspeople.
Defense Modifier +2; Unrest –1.
Black Market (50 BP; must be adjacent to 2 houses): A number of shops with secret and usually illegal or dangerous wares.
Town base value +2,000; 2 minor items, 1 medium item, 1 major item; Economy +2, Stability +1; Unrest +1.
Brewery (6 BP): A building for beermaking, winemaking, or similar use.
Loyalty +1, Stability +1.
Brothel (4 BP; must be adjacent to 1 house): A place to pay for companionship of any sort.
Economy +1, Loyalty +2; Unrest +1.
Caster’s Tower (30 BP): The home and laboratory for a mage.
3 minor items, 2 medium items; Economy +1, Loyalty +1.
Castle (54 BP): The home of the clans chief and the heart of the towns defenses.
Halves cost of Mansion or Town Square in same town; Economy +2, Loyalty +2, Stability +2; Defense Modifier +8; Unrest –4; limit one per town.
City Wall (8 BP): City walls do not occupy a city block — rather, purchasing a city wall fortifies one of a district’s four outer borders. A city wall cannot be built on a water border.
Defense Modifier +4; Unrest –2.
Dump (4 BP): A centralized place to dispose of refuse.
Loyalty +1, Stability +1.
Granary (12 BP): A place to store grain and food.
Loyalty +1, Stability +1.
Graveyard (4 BP): A plot of land to honor and bury the dead.
Economy +1, Loyalty +1.
Guildhall (34 BP; must be adjacent to 1 house): A large building that serves as headquarters for a merchant companies or similar organization.
Town base value +1,000 gp; halves cost of Pier, Stable, and Tradesman in same city; Economy +2, Loyalty +2.
Herbalist (10 BP; must be adjacent to 1 house): The workshop and home of a gardener, healer, poisoner, or creator of potions.
1 minor item; Loyalty +1, Stability +1.
Hero's Grave (4 BP): The resting place of a famous hero, often the founder of the clan.
Loyalty +2, Unrest -1.
House (3 BP): You help the people in the town to build better houses increasing the standard of living in the town. Houses serve as prerequisites for many other buildings. The first house you build during any Improvement Phase does not count against the total number of buildings you
can build during the phase.
Unrest –1.
Inn (10 BP; must be adjacent to 1 house): A place for visitors to spend the night.
Town base value +500 gp; Economy +1, Loyalty +1.
Keep (27 BP): A smaller version of the castle. Usually the home of the chief or one of his most loyal followers entrusted with governing the area.
Economy +1, Loyalty +1, Stability +1, Defense Modifier +4, Unrest -2, limtited to one Keep or Castle per town.
Mansion (10 BP): A single huge manor housing a rich family and its slaves and servants.
Stability +1.
Market (48 BP; must be adjacent to 2 houses): An open area for mercantile pursuits, traveling merchants, and bargain hunters.
Town base value +2,000 gp; halves cost of Black Market, Inn, and Shop in same town; 2 minor items; Economy +2, Stability +2.
Mill (6 BP; must be next to a water border): A building used to cut lumber or grind grain.
Economy +1, Stability +1.
Palisade (3 BP): A much cheaper alternative to stone walls.
Defense Modifier +2, Unrest -1.
Piers (16 BP; must be adjacent to a water border): Warehouses and workshops for docking ships and handling cargo and passengers.
Town base value +1,000 gp; +1 Economy, +1 Stability.
Shop (8 BP; must be adjacent to 1 house): A general store.
Town base value +500 gp; Economy +1.
Shrine (8 BP): A small shrine or similar holy site.
1 minor item; Loyalty +1; Unrest –1.
Smith (6 BP): An armor smith, blacksmith, or weapon smith.
Economy +1, Stability +1.
Stable (10 BP; must be adjacent to 1 house): A structure for housing or selling horses and other mounts.
Town base value +500 gp; Economy +1, Loyalty +1.
Tannery (6 BP; cannot be adjacent to a house): A structure that prepares hides and leather.
Economy +1, Stability +1.
Tavern (12 BP; must be adjacent to 1 house): An eatery or drinking establishment.
Town base value +500 gp; Economy +1, Loyalty +1.
Temple (32 BP): A large place of worship dedicated to a deity.
Halves cost of Graveyard and Shrine in same town; 2 minor items; Loyalty +2, Stability +2; Unrest –2.
Tenement (1 BP): A staggering number of low-rent, cheap housing units. Tenements count as houses for the purpose of fulfilling building requirements, but building too many tenements can increase a kingdom’s Unrest quickly.
You can build a house over an existing tenement for 2 BP. Unrest +2.
Town Square: A central meeting place where the elders and leaders of the town gather to discuss matters of public concern and where the chief adresses his people.
Loyalty +1, Stability +1.
Tradesman (10 BP; must be adjacent to 1 house): A shopfront for a tradesman, such as a baker, butcher, candle maker, cooper, or rope maker.
Town base value +500 gp; +1 Economy, +1 Stability.
Warrior Hall (20 BP): A central meeting hall were the accomplished full time warriors of the clan gather and train. Since this is basically the headquarter for military forces in the area, it makes the town a lot more secure. It also promotes pride in the clans might and displays the forces that the chief commands.
Defense Modifier +2, Loyalty +1, Stability +1, Unrest -1.
Watchtower (6 BP): A tall structure that serves as a guard post and landmark.
+1 Stability; +2 Defense Modifier; Unrest –1.
Waterfront (90 BP; must be adjacent to a water border): A port for arrival and departure when traveling by water, facilities for building ships, and a center of commerce.
Town base value +4,000 gp; 3 minor items, 2 medium items, 1 major item; halves cost of Guildhall and Market in same town, halves Loyalty penalty for tax edicts; Economy +4; limit one per town.
Witch Hut (10 BP, may not be adjacent to more than one house): A lesser version of the casters tower. A witch can provide vital services, but is generally mistrusted.
2 minor items; Economy +1, Unrest +1.