There is also a fourth floor, but I think it is merely the battlements of the tower and the portion of the keep on the left-hand side.
If you do a search of Tamworth Castle, you will find several photos, including some nice aerial pictures. I sometimes have a hard time visualizing old castles, without some photos to fall back on.
The nice thing about the Tamworth Castle site is that they have easily two dozen or more different photos, including many interior shots, to help you visualize the rooms. That helps when trying to describe them to your players.