KJV:

10 The chambers were in the thickness of the wall of the court toward the east, over against the separate place, and over against the building.

NASB:

10 In the thickness of the wall of the court toward the east, facing the separate area and facing the building, there were chambers.

"The separate place" is an area of 100 x 100 cubits where the altar is located. "Building" is the Temple. The width of the space between the line of the front facade of the Temple and the gate allows you to place a building for the Kohanim with a width of 30 cubits.