You are forbidden to build a cooling system and no big investment is allowed. Your room is about 27-30 celcius and it takes hours until the room temperature is about 25-26 celcius again, making tiresome sleep. This question is related to Apartment on the top floor gets very hot - cheap, eco friendly ways to keep the place cool? and lifehacks here, summary. The apartment has three floors where the top floor is very hot with sleeping areas. I welcome all kind of alternatives and serious DIY solutions.
What are alternative ways to cool your body in hot room?