It's crucial to understand that if we let a person that build a shelter keep it for eternity then that person can build many shelters such that there will be no land left for other people to build their shelters on.
This is why in a society free from theft, one must build or make something for exchange to get things you want.
I don't see why buying two plots and building two houses entitles someone else to one of them.
There's no free land, but there is cheap land, especially in deserts. Simply owning land might not be as nice as you imagine