Does anyone have any experience with an open sky atrium? I have a small 45 sq ft atrium in my house, with an exterior wall on one side and 3 sliding glass doors on the others. It is open to the elements and currently there are a few plants growing wild inside. The ground is covered in mulch. We just bought the house a little over a year ago and have not had the chance to work on it yet.

Last night it rained pretty bad and the atrium filled with water and flooded the house. There does not appear to be any way for water to drain out other than absorption into the ground. Any suggestions on what would help it drain better? More or less plants? Rocks or mulch? Any insight would be appreciated.