How to make money as Bretonnia

Bretonnia's fastest-paying building in Total War: Warhammer III is the Fields (Farming, level 1): 500 gold for +300 gold a turn, its cost back in 1.7 turns once built. The most gold from one building slot is the Landed Estate at +600 a turn (3,000 gold to build the chain that far, back in 5 turns). 55 Bretonnia 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).

1FieldsFarming 1 · 500 gold → +300 a turn · Any settlement1.7turns
2Gem MineGem Mining 2 · 1,000 gold → +400 a turn · Region with the resource2.5turns
3Gold MineGold Mining 2 · 1,000 gold → +400 a turn · Region with the resource2.5turns
4Weaving HouseIndustry 1 · 500 gold → +200 a turn · Any settlement2.5turns
5Animal StoreTusks 1 · 500 gold → +100 a turn · Region with the resource5turns
6Brine Mining PitSaltmaking 1 · 500 gold → +100 a turn · Region with the resource5turns

Most gold per building slot

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

1Landed EstateFarming 3 · 1,500 gold → +600 a turn · Any settlement+600a turn
2Gemcutter's WorkshopGem Mining 3 · 2,000 gold → +600 a turn · Region with the resource+600a turn
3Gold SmelterGold Mining 3 · 2,000 gold → +600 a turn · Region with the resource+600a turn
4Bretonnian Fishing PortPort 3 · 6,000 gold → +500 a turn · Port settlement+500a turn
5TailorsIndustry 3 · 1,500 gold → +400 a turn · Any settlement+400a turn
6Alchemy WorkshopMedicine Production 3 · 2,000 gold → +200 a turn · Region with the resource+200a 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 Bretonnia building that makes gold (55)

#
1	Fields	Farming	1	500	1	300	1.70	—	2.70	Any settlement
2	Farm	Farming	2	1,000	2	450	2.20	6.70	4.20	Any settlement
3	Gem Mineshaft	Gem Mining	1	500	2	200	2.50	—	4.50	Region with the resource
4	Gem Mine	Gem Mining	2	1,000	3	400	2.50	5	5.50	Region with the resource
5	Gold Mining Pit	Gold Mining	1	500	2	200	2.50	—	4.50	Region with the resource
6	Gold Mine	Gold Mining	2	1,000	3	400	2.50	5	5.50	Region with the resource
7	Landed Estate	Farming	3	1,500	3	600	2.50	10	5.50	Any settlement
8	Weaving House	Industry	1	500	2	200	2.50	—	4.50	Any settlement
9	Gemcutter's Workshop	Gem Mining	3	2,000	4	600	3.30	10	7.30	Region with the resource
10	Gold Smelter	Gold Mining	3	2,000	4	600	3.30	10	7.30	Region with the resource
11	Clothier	Industry	2	1,000	3	300	3.30	10	6.30	Any settlement
12	Tailors	Industry	3	1,500	4	400	3.80	15	7.80	Any settlement
13	Exotic Animal Tamer	Exotic Animals	1	500	1	100	5	—	6	Region with the resource
14	Cinnabar Mining Pit	Dye Production	1	500	1	100	5	—	6	Region with the resource
15	Iron Mining Pit	Iron Mining	1	500	2	100	5	—	7	Region with the resource
16	Stone Cutter	Marble Quarry	1	500	1	100	5	—	6	Region with the resource
17	Herb Gatherer's Camp	Medicine Production	1	500	1	100	5	—	6	Region with the resource
18	Obsidian Quarry	Obsidian Quarry	1	500	1	100	5	—	6	Region with the resource
19	Grazing Pastures	Pastures	1	500	1	100	5	—	6	Region with the resource
20	Clay Pit	Pottery Production	1	500	1	100	5	—	6	Region with the resource
21	Brine Mining Pit	Saltmaking	1	500	1	100	5	—	6	Region with the resource
22	Spice Market	Spice Trading	1	500	1	100	5	—	6	Region with the resource
23	Woodman's Hut	Woodlands	1	500	1	100	5	—	6	Region with the resource
24	Orchards	Orchards	1	500	1	100	5	—	6	Region with the resource
25	Animal Store	Tusks	1	500	1	100	5	—	6	Region with the resource
26	Exotic Animal Pen	Exotic Animals	2	1,000	2	150	6.70	20	8.70	Region with the resource
27	Cinnabar Mine	Dye Production	2	1,000	2	150	6.70	20	8.70	Region with the resource
28	Iron Mine	Iron Mining	2	1,000	3	150	6.70	20	9.70	Region with the resource
29	Marble Quarry	Marble Quarry	2	1,000	2	150	6.70	20	8.70	Region with the resource
30	Exotic Hothouse	Medicine Production	2	1,000	2	150	6.70	20	8.70	Region with the resource
31	Obsidian Trinket Maker	Obsidian Quarry	2	1,000	2	150	6.70	20	8.70	Region with the resource
32	Livestock Pens	Pastures	2	1,000	2	150	6.70	20	8.70	Region with the resource
33	Pottery Maker	Pottery Production	2	1,000	2	150	6.70	20	8.70	Region with the resource
34	Brine Mine	Saltmaking	2	1,000	2	150	6.70	20	8.70	Region with the resource
35	Spice Trading Post	Spice Trading	2	1,000	2	150	6.70	20	8.70	Region with the resource
36	Timber Mill	Woodlands	2	1,000	2	150	6.70	20	8.70	Region with the resource
37	Vineyard	Orchards	2	1,000	2	150	6.70	20	8.70	Region with the resource
38	Tusk Market	Tusks	2	1,000	2	150	6.70	20	8.70	Region with the resource
39	Exotic Animal Market	Exotic Animals	3	2,000	3	200	10	40	13	Region with the resource
40	Dyemaker	Dye Production	3	2,000	3	200	10	40	13	Region with the resource
41	Iron Smelter	Iron Mining	3	2,000	4	200	10	40	14	Region with the resource
42	Mason	Marble Quarry	3	2,000	3	200	10	40	13	Region with the resource
43	Alchemy Workshop	Medicine Production	3	2,000	3	200	10	40	13	Region with the resource
44	Obsidian Amulet Carver	Obsidian Quarry	3	2,000	3	200	10	40	13	Region with the resource
45	Cattle Ranch	Pastures	3	2,000	3	200	10	40	13	Region with the resource
46	Kilns	Pottery Production	3	2,000	3	200	10	40	13	Region with the resource
47	Saltworks	Saltmaking	3	2,000	3	200	10	40	13	Region with the resource
48	Eastern Bazaar	Spice Trading	3	2,000	3	200	10	40	13	Region with the resource
49	Lumberyard	Woodlands	3	2,000	3	200	10	40	13	Region with the resource
50	Vintner	Orchards	3	2,000	3	200	10	40	13	Region with the resource
51	Tusk Compound	Tusks	3	2,000	3	200	10	40	13	Region with the resource
52	Bretonnian Fishing Harbour	Port	2	3,000	4	300	10	15	14	Port settlement
53	Bretonnian Fishing Port	Port	3	6,000	6	500	12	30	18	Port settlement
54	Bretonnian Fishery	Port	1	1,500	2	100	15	—	17	Port settlement
55	Brothel	Hostelry	4	4,000	5	50	80	80	85	Any 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	Hamlet	Provincial Capital	1	1,000	—	40	—
2	Hamlet	Minor Settlement	1	1,000	—	40	—
3	Village	Provincial Capital	2	2,000	1	60	100
4	Village	Minor Settlement	2	2,000	1	60	100
5	Town	Provincial Capital	3	4,000	2	80	200
6	Town	Minor Settlement	3	4,000	2	80	200
7	City	Provincial Capital	4	8,000	4	100	400
8	Duchy Capital	Provincial Capital	5	16,000	5	120	800

Every level's full effects: Bretonnia buildings.