how create a loft(wardrobe in top of room)

[ploufus]

Most WC here use top 1 meter as a closed with a door outside in corridor as a wardrobe/closit style

How can i split a room in half with extra "floor" for that ?

[Keet]

You can place doors and windows above each other in the same wall. Just elevate one above the other.
Use a box as the ceiling for the WC and elevate it to the bottom of the extra closet.
Adjust the height of a door or create a new one and elevate that door above the WC door.