You start the game with a rather small farmhouse in Stardew Valley, but it's possible to upgrade this to eventually become very big, with several different rooms, including a kitchen, a room for children, and a cellar.
In order to upgrade your house in Stardew Valley, go to Robin the carpenter and talk with her when she is in her shop. This will give you the option to open a "Upgrade House" menu. Click on this, and she will tell you the cost to upgrade your house.
The first upgrade adds a big kitchen, and cost the following:
- 450x Wood
The second upgrade adds two more rooms; one for your children, and one that's empty. It cost the following:
- 150x Hardwood.
The third and final upgrade adds a cellar under your house, and here you can store casks to increase the quality of things like alcohols and cheeses. It cost the following:
And that's all the upgrades you can purchase. You can also get an additional room for your spouse, which will happen automatically when you marry a character in the game.