There are a total of five home extensions, which, all-in-all, will cost you 56,500G and 2,620 pieces of wood, but it's worth it! You can't choose which extension you get; you HAVE to get them in the order listed below. Renovations cost money, obviously, so it isn't something you'll be able to do right away. You also need lumber to build the extensions. You can get wood pieces by chopping tree stumps in the forest.
Once you have enough money and lumber, you must talk to Gotz, the carpenter who lives in the Spring. Talk to him when his carpentry is open and hire him to do the extension for you. Gotz will take three days to complete each extension.
The Chicken Coop
Wood: 420 pieces
When you let Gotz build this extension, you receive space for five more chickens. This extension is required if you want to marry Rick.
First House Extension
Wood: 370 pieces
When Gotz completes this upgrade, you will have a kitchen with a fridge and a cabinet. Also your television set becomes better looking from your original. The kitchen is well worth it.
First Barn Extension
Wood: 500 pieces
When Gotz completes this upgrade, this will give you space for 10 extra animals, adding up to 20 in total. Plus, it gives you another place for a pregnant sheep or cow to stay until it has its baby.
Second House Extension
Wood: 750 pieces
When Gotz completes this upgrade, your house comes with more kitchen and cabinet space, a living room, a fireplace, another bed, a better looking TV.
Wood: 580 pieces
The greenhouse sits right next to your house. It works the same way the greenhouse in Harvest Moon 64 works, except it's smaller; you can grow any crops you want in here, during any season. It's expensive, but can easily be torn down by hurricanes or winter storms - In which case, unfortunately, you'd have to replace it. Orange Cup seeds can only grow in here.