Place a ground
Go to the Shopping Center, upstairs, and click on a floor to have it in your inventory.
Click on the ground object in your inventory (with the left mouse button),
move your mouse over your empty land (without releasing the mouse button),
and then release the mouse button. Your ground will then appear on the land.
To place your floor right in the middle of the land,
right-click on your floor and choose the menu OBJECT > EDIT.
Change 'OWNER' to 'POSITION'. Then type in X and Y the value 32.768 and in Z the value 0
To block your land (to avoid damaging it by accident later on),
change 'POSITION' to 'OWNER' and click LOCKED.
To continue, read the chapter : extend your rent