Efficient buildings you buy with gold
Gold on the farm doesn't go only into decorations, it also buys upgraded versions of the regular production buildings – the chicken coop, pigsty, cowshed, orchards, barn or windmill. You can spot these buildings by the word Efficient, Fancy, Deluxe, Spacious or Fertile in the name, and they replace their plain sibling in the same spot. I've written down what each of them does, what farm level you need to build it and how much gold and how many upgrade levels it takes, mainly on the Main farm, where there are the most of them.
Efficient buildings are the most reliable way to spend gold, because a boost to output or capacity you pay for once keeps running with no further spending, unlike a one-off speed-up. It pays to work through them one at a time according to what is holding the farm back right now, instead of reaching straight for the priciest pieces.
An efficient building replaces the plain one and raises yield or capacity

Gold buys an upgraded version of a regular production building – you can tell it by the word Efficient, Fancy, Deluxe, Spacious or Fertile in the name. A building like that replaces its plain sibling in the same spot and does exactly the same job, just in bigger amounts.
The Efficient chicken coop, Efficient pigsty and Efficient cowshed still deliver eggs, pigs or milk along with manure, only more of it than the ordinary version of the animal building. The Efficient windmill grinds feed for the animals and squeezes more out of a batch of raw material than a regular mill, the Efficient apple orchard takes fertilizer from the silo and hands me more apples and leaves than a plain orchard, and the Fertile field keeps enough crops coming so the queue for raw materials never jams up in the production buildings. The Spacious barn raises storage capacity instead of yield and can be upgraded further, and the Fancy house puts up more workers than a regular house, and all that luxury keeps them happier too.
The Main farm has fourteen efficient buildings you can buy with gold
An overview of the production buildings you buy with gold on the Main farm – the cost of the first level, the farm level you need to build them and how many levels they can be upgraded to.
| Building | First level cost | From farm level | Max. level |
| Spacious barn | 450 Gold | 0 | 12 |
| Fertile field | 350 Gold | 0 | 11 |
| Efficient windmill | 2500 Gold | 0 | 10 |
| Efficient chicken coop | 150 Gold | 0 | 10 |
| Fancy house | 250 Gold | 1 | 10 |
| Efficient apple orchard | 400 Gold | 5 | 9 |
| Efficient pigsty | 200 Gold | 7 | 10 |
| Efficient cowshed | 300 Gold | 13 | 10 |
| Water tower | 1300 Gold | 14 | 5 |
| Efficient cherry orchard | 500 Gold | 15 | 9 |
| Efficient sheep pen | 200 Gold | 17 | 11 |
| Efficient vineyard | 400 Gold | 17 | 9 |
| Workshop | 1600 Gold | 19 | 5 |
| Water filtration system | 1560 Gold | 39 | 5 |
The Water tower, Fancy house, Workshop and Water filtration system aren't tied to the Main farm – the same buildings for the same price and with the same level requirement can be built on the Gourmet farm and the Flower farm as well.
Other farms have efficient buildings of their own, just not as many

The Gourmet farm adds animal buildings and orchards of its own – the Efficient donkey stable, Efficient duck coop, Efficient goat stable, Efficient rabbit hutch, Efficient peach orchard, Efficient almond orchard and Fertile garden, plus the Efficient water mill and three textile buildings (Efficient dye factory, Efficient spinning factory, Efficient clothing factory). Most of them unlock from farm level 19 upwards, and the textile trio and the Efficient water mill cost 3000 Gold for the first level.
The Flower farm has its own orchards and apiary – the Fertile meadow, Efficient olive grove, Efficient citrus orchard and Efficient apiary – but those unlock only from level 38 upwards, and the Efficient citrus orchard not until level 61. The Obsidian farm has a set of four of its own (Fancy cabin, Spacious storehouse, Fertile volcanic field, Efficient feed kitchen), which you won't reach before level 114. The Island farm, Viking farm, Festive farm, Northern lights farm and Candy farm get only an upgraded version of the house out of the efficient buildings (on the Candy farm it's called the Lovely mobile home), so capacity and yield there have to be solved some other way.
Cheaper buildings that unlock early are worth getting first

Gold is a limited resource, so I rank the buildings by whatever is holding my farm back the most right now. It makes sense to start with what limits the farm as a whole – the Spacious barn for storage and the Fancy house for workers – because a shortage of space or manpower slows down absolutely everything I do on the farm. Only after that do I reach for specific animal buildings and orchards, depending on which raw material my production buildings are burning through fastest.
The other thing I look at is the farm level a building needs at all – there's no point saving gold for the Efficient citrus orchard when the farm is nowhere near level 61. The cheaper buildings available from lower levels, like the Efficient chicken coop, Efficient pigsty or Efficient apple orchard, paid off for me first, while pricey builds such as the Workshop or the Water filtration system came later, once I had gold to spare.
Buildings and products mentioned in the text
HouseMain farm · from level 29 · 5 × 5
Chicken coopMain farm · 5 × 5
Fancy houseMain farm · from level 1 · 5 × 5
PigstyMain farm · from level 7 · 7 × 6
BarnMain farm · 7 × 6
Efficient citrus orchardFlower farm · from level 61 · 10 × 10
Efficient apple orchardMain farm · from level 5 · 7 × 7
Water filtration systemMain farm · from level 39 · 4 × 4