If you don't add a ceiling, a second room upstairs, or a roof, this can make Sims more vulnerable to cold or heat. how to add a ceiling: Open build mode, go into the Walls and Empty rooms section and pick the - Flat Square - option, place it on the top of the room as a ceiling, this will ensure the room will work correctly.
for a room to work correctly, after setting it up in the game, you will have to add a ceiling or another room on the top as a second floor.
How to set up a room with platforms in the game:
