1 Chronicles 28:11-12 (NASB)
11 Then David gave to his son Solomon the plan of the porch of the temple, its buildings, its storehouses, its upper rooms, its inner rooms and the room for the mercy seat; 12 and the plan of all that he had in mind, for the courts of the house of the LORD, and for all the surrounding rooms, for the storehouses of the house of God and for the storehouses of the dedicated things;
The Scripture has no description concerning the location of these upper rooms. However some scholars have conjectured where they would be.
The interior measurements of the temple were 60 cubits (90 feet) in length and 30 cubits (45 feet) in height and 20 cubits (30 feet) in width (2 Chronicles 3:3). Concerning the Most Holy Place, it was a perfect cube, 20 cubits (30 feet) by 20 cubits by 20 cubits (2 Chronicles 3:8).
This leaves a space above the Most Holy Place which was 10 cubits (15 feet) high, 20 cubits (30 feet) wide and 20 cubits (30 feet) long. Some have therefore proposed that this space above the Most Holy Place would be the location of the upper rooms.
However there were problems with the above proposal:
The fact that the Bible does not describe in details about the upper rooms leads me to believe that the upper rooms were part of the side chambers already mentioned. And since they were described as upper, they must be at the third story.
Now they were specifically mentioned because this area had a different purpose - it was used for storing the treasures. We know that because the inside of the upper rooms were overlaid with gold (2 Chronicles 3:9). And for that purpose, it must be secured also. For maximum security, the upper rooms would most likely be located at the north side of the third story.