A Roulette Chamber is an object in the game. They cost money to activate. When activated, random Items will show up in the chamber; pressing the activation button again will stop the random selection of items and give you the item currently in the chamber.
The random selection of items will gradually speed up; after enough time, the game will randomly give you an item because the selection is too fast.
A strategy with Roulette Chambers called "pause buffering" exists where you repeatedly pause the game once you activate the Roulette Chamber; once you see an item you want, you can un-pause and then immediately select the item.