Construct buildings from the “Infrastructure” tab and complete the Super-quests (Superzilla, Nessie, Genie, etc.) to increase your population limit.

After that, building new houses will attract new citizens to your city.

Once you get the correct population that a building says, then it will unlock for you and then you can buy and place them.

Example: Here you can see that the coffee shop needs population of 400. Once you have enough population, then it will unlock for you.

you find the population on the neighbor bar.