The Patio can be accessed either from the Upper Gallery of the Hall of Heroes (the door is located just above the main entrance) or from the Safehouse. Note that you can't access the Safehouse from the Patio until you got the Key from Auryen because the doors are key-locked.
There's a stairway to the right of the entrance to the Dragonborn Gallery that also leads up to the Patio.
At first the Patio is empty and provides just a view over Solitude and its harbor. After buying the two upgrades from Bits and Pieces in Solitude (Safehouse Patio Seating Receipt and Safehouse Patio Greenhouse Receipt), an awning with table and chairs as well as a greenhouse is added.
The awning is merely only a visual upgrade where you can sit on the patio and relax.
The greenhouse, however, features the regular Fertile Soil system that The Elder Scrolls V: Hearthfire provides. Here you can plant and harvest vegetables and ingredients.
