"The size of the chamber (after allowing suitably in each part for the incrustation of salt) is on an average 205.85 wide, and 226.47 long, 184.47 high on N. and S. walls, and 245.1 high to the top of the roof ridge on E. and W. walls." (Petrie 1883: 66)
Here the height to the roof ridge is 245.1" / 6.225 m / about 11.89 cubits. Petrie's mean height measurements are taken from the footing of fine stone at the present rough floor level - the final layer of finished floor blocks would have been laid on this footing. He also gives the height from the floor level of the niche N side to the roof ridge as 245.7" / 6.24 m / about 11.92 cubits.
The intended height of the finished chamber may have been 11 cubits, which is also the length of the chamber. This means the finished floor level would have been about the height of the floor level in the horizontal passage before the step down leading to the chamber. The height of the N and S walls would have been 8 cubits. Alternatively the height of the chamber to the roof ridge may have been 11.18 cubits - about the same as the height of the sarcophagus chamber.
CT