Don't understand why the stand didn't have a sloping extra block at each end, would of looked a lot better, having said that it looks fuckin great.
The new third tier is completely "maxed out" in terms of both height and width, the limitations being the cables running down from the internal cable "ring" (which runs around the front of the four stands). This cable is still in place despite the construction of a new roof as the ring supports the other three stands. If you view the picture below (courtesy of @gingerwig) you'll see the aforementioned cables running within a few metres of the new tier. From the top of the new tier you'll see the cables running back through the stand and down to the original support masts. Pretty amazing engineering and design to shoehorn a 6k seat stand on top of an existing structure whilst simultaneously holding live events every other week throughout 90% of the construction project. I for one think it's a triumph.
The current cable support restricts the design and therefore capacity for now. I expect the entire roof structure will be different once the east and west stands are expanded. Here's that photo...