The Mayor of Kilima has visited and graced your new home with an expansion. Access the Housing menu while on your plot, and place the blueprint.
Someone else has come to visit. Why don't you see if they have anything that can help finish your house?
Now that you have placed the frame for your small room, you can finish it by depositing bricks and planks at the build site. You'll need a smelter and sawmill to refine the materials!
You've finished your extra room, and it seems Ashura's come to visit.
Ashura: Good to see you, Player. I just wanted to stop by and see how things were coming along.
Ashura: Seems like you've already started to make friends in the valley. I've heard nothing but good things from the folks you've met.
Ashura: I brought you some new wallpaper and flooring, too. Just in case you feel like switching things up!
Ashura: I also wanted to let you know that if you want to keep adding to your house, you'll want to stop by City Hall.
Ashura: Kenyatta's usually behind the register, and she can set you up with expansion permits, new rooms, and even additional buildings.
Ashura: Now I'd better start heading back. Not as spry as I used to be, and these hills feel like they got a little steeper...