This is all my opinion and my damn brain.
Asch. Asch is most likely to have a king-sized bed, trophy's and crowns.
Rhys. I'd expect Rhys to have a twin-sized bed, books and his staff.
Pierce. Due to Pierce's actions I say his room would have a twin-sized bed and swords.
Leif. Leif is most likely to also have a king-sized bed, a tank (cus why not) and some masks to scare Noi?
Noi. Based on how he acts I think he would have a twin-sized bed (ignore it's king-sized please) stuffed animals and plants.