Heres some concept art for the room of requirement door and interior.
The inside looks are first seen in The half blood prince where Draco Malfoy is repairing the Vanishing cabinet.
This concept was also used in deathly hallows part 2 where harry tries to seek up an Horcrux hidden in many years of storage.
as you can see, there models of Mountain trolls, The chess pieces and Mad-eyes spectacles from the his' version of the Defense against the Dark arts classroom.
The entrance to the Room of requirement.
The last picture is computer generated, and if you look closely you can see the "mountains" of stuff is made of different sized boxes produced in Illustrator.