Once you have created your floor, you can create a balcony. To create your balcony, select the Partition tool in the Build > Walls and partitions menu. Draw your balcony on the room of your choice.
Note: You can choose the thickness before you start drawing by changing the 7 shown in the image below.
Next, you need to set the Properties of the walls.
Untick Up to ceiling and enter the desired height for your railings. Do this for all the balcony walls.
Now switch to 3D view. You can decorate your balcony for a better render. We have applied a metal effect below.
Finally, you need to remove the ceiling from your balcony. To do so, go back to 2D view. Click on your balcony and then on its Properties. Deselect Ceiling.
While you're in this menu, you can also choose the Type of room (changing it to Balcony), give it a Name and adjust the Slab thickness.