How to make money as Undead Legions

Undead Legions's fastest-paying building in Total War: Warhammer III is the Cursed Gemstone Mineshaft (Gem Mining, level 1): 1,750 gold for +500 gold a turn, its cost back in 3.5 turns once built. The most gold from one building slot is the Currents of Emptiness at +550 a turn (12,500 gold to build the chain that far, back in 22.7 turns). 17 Undead Legions building levels make flat income, patch 9.0.4.

Fastest payback

Turns of income to earn the building's cost back (each chain's fastest level).

1Cursed Gemstone MineshaftGem Mining 1 · 1,750 gold → +500 a turn · Region with the resource3.5turns
2Gold Mining PitGold Mining 1 · 1,750 gold → +400 a turn · Region with the resource4.4turns
3The Place of EndingsDark Ritual Site 1 · 1,000 gold → +150 a turn · Any settlement6.7turns
4Dust RepositorySpice Trading 1 · 1,750 gold → +250 a turn · Region with the resource7turns
5Pits of Clay and BonePottery Production 1 · 1,750 gold → +250 a turn · Region with the resource7turns
6Cursed FieldsPastures 1 · 1,750 gold → +200 a turn · Region with the resource8.8turns

Most gold per building slot

Income of each chain's top level; the line shows that level's own cost.

1Currents of EmptinessDark Ritual Site 5 · 4,000 gold → +550 a turn · Any settlement+550a turn
2Cursed Gemstone MineshaftGem Mining 1 · 1,750 gold → +500 a turn · Region with the resource+500a turn
3Silent ShipyardsPort 3 · 5,000 gold → +500 a turn · Port settlement+500a turn
4Gold Mining PitGold Mining 1 · 1,750 gold → +400 a turn · Region with the resource+400a turn
5Dust RepositorySpice Trading 1 · 1,750 gold → +250 a turn · Region with the resource+250a turn
6Pits of Clay and BonePottery Production 1 · 1,750 gold → +250 a turn · Region with the resource+250a turn

COMPUTEDIncome = the level's flat gold per turn (the game's “Income generated” effects on the building itself, table building_effects_junction) minus its upkeep (building_levels.upkeep_cost). Payback = cost (create_cost) ÷ income. Upgrade payback = the level's cost ÷ the income it adds over the level below. “Gold back by turn” = build turns (create_time) + payback, counted from the order. Chain total = every level's cost up to this one, and its payback = that total ÷ income. Patch 9.0.4.

ASSUMPTIONS

Base values: technologies, lord skills, commandments, campaign difficulty and faction effects that change income or building costs are not counted.
Percentage boosts (“+4% income from all buildings in the province”, “+20% (local region)”) are not in the payback: they depend on the buildings they boost. They are listed below with the income those buildings need to make.
Conditional income (“When Control is 75 or more”, “When enemy Lord is present”…) is not counted; listed below in the game's words.
Resource buildings need a region with that resource; ports need a port settlement. A slot can hold one building, so late in a campaign gold per slot matters more than payback.

Every Undead Legions building that makes gold (17)

#
1	Cursed Gemstone Mineshaft	Gem Mining	1	1,750	2	500	3.50	—	5.50	Region with the resource
2	Gold Mining Pit	Gold Mining	1	1,750	2	400	4.40	—	6.40	Region with the resource
3	The Place of Endings	Dark Ritual Site	1	1,000	1	150	6.70	—	7.70	Any settlement
4	Leeching Obelisks	Dark Ritual Site	2	1,750	2	250	7	17.50	9	Any settlement
5	Pits of Clay and Bone	Pottery Production	1	1,750	2	250	7	—	9	Region with the resource
6	Dust Repository	Spice Trading	1	1,750	2	250	7	—	9	Region with the resource
7	Walls of Eternity	Dark Ritual Site	3	2,500	3	350	7.10	25	10.10	Any settlement
8	Vistas of Desolation	Dark Ritual Site	4	3,250	4	450	7.20	32.50	11.20	Any settlement
9	Currents of Emptiness	Dark Ritual Site	5	4,000	5	550	7.30	40	12.30	Any settlement
10	Red Pit	Dye Production	1	1,750	2	200	8.80	—	10.80	Region with the resource
11	Cursed Fields	Pastures	1	1,750	2	200	8.80	—	10.80	Region with the resource
12	Field of Plinths	Control	1	1,000	1	100	10	—	11	Any settlement
13	A Hushed Tavern	Trade Posts	1	1,000	1	100	10	—	11	Any settlement
14	Necromantic Light	Corruption	1	1,000	1	100	10	—	11	Any settlement
15	Ever-rotting Pier	Port	1	1,000	1	100	10	—	11	Port settlement
16	Shoals of Hollow Promise	Port	2	3,000	3	300	10	15	13	Port settlement
17	Silent Shipyards	Port	3	5,000	5	500	10	25	15	Port settlement

Main building levels

Settlement upgrades make gold too, but they also cost growth (population surplus) and open building slots, so payback alone undersells them. Province capitals and minor settlements are separate chains.

#
1	Valley of Open Tombs	Burial Chambers	1	1,000	—	50	—
2	Half-drowned Cove	Pirate Cove	1	1,000	—	50	—
3	Vampiric Enclave	Mausoleum	1	1,000	—	50	—
4	Crypt Colony	Necropolis	1	1,000	—	100	—
5	City of Catacombs	Necropolis	2	2,000	—	175	26.70
6	Sepulchral Sprawl	Necropolis	3	3,500	—	250	46.70
7	Charnel Scape	Necropolis	4	5,000	—	325	66.70
8	Great Necropolis	Necropolis	5	10,000	—	400	133.30

Conditional income

The Place of Endings (Dark Ritual Site 1): +50 a turn — When Devastated by the Ritual of Undeath
Leeching Obelisks (Dark Ritual Site 2): +100 a turn — When Devastated by the Ritual of Undeath
Walls of Eternity (Dark Ritual Site 3): +150 a turn — When Devastated by the Ritual of Undeath
Vistas of Desolation (Dark Ritual Site 4): +200 a turn — When Devastated by the Ritual of Undeath
Currents of Emptiness (Dark Ritual Site 5): +250 a turn — When Devastated by the Ritual of Undeath
Ever-rotting Pier (Port 1): +50 a turn — When Devastated by the Ritual of Undeath
Shoals of Hollow Promise (Port 2): +150 a turn — When Devastated by the Ritual of Undeath
Silent Shipyards (Port 3): +250 a turn — When Devastated by the Ritual of Undeath

Every level's full effects: Undead Legions buildings.