The invention relates to a method for modifying a room unit for a marine vessel or other corresponding structure, which room unit (1) is provided with wall portions (8), a roof portion and a floor portion in order to form a first space (2), and which room unit is provided with an arrangement for a second space (3). In order to be able to convert the room unit for different types of use in view of the prevailing circumstances, the room unit (1) is provided with a partition element arrangement (4), which when placed in a first position (A) separates the first space (2) and at least a part of the second space (3) to form a cabin unit (5) and a thereto attached balcony unit (6), and, which when placed in a second position (B) joins the first space (2) and the and at least a part of the second space (3) to form an integral cabin unit (7).