it's pretty hopeless for good photography, AP. The lower (enclosed) floor has double glass walls most of the way round - not double glazing, just two separate sheets of glass a foot or two part; plus there are pillars everywhere, painted white. So there's a reflection nightmare. There are one or two spots with just a single pane and if it's clean you can get the odd decent shot through it.
Upstairs is openish, on the corners at least, and partly single glazed, as I recall. But there's hardly anywhere to take a photo with no obstruction at all. On the outside bits you could have your camera on a pole reaching above the glass (which is a good six feet high), and there are a couple of gaps between sheets where you could squeeze the lens of a compact.
But that's about it. The building wasn't actually intended to be camera-friendly (even though everyone who goes up there will have one); I suspect the public gallery was an afterthought.
Nice views though. But much of the view to the south will be a mix of sun and haze/cloud... which a skilled photograopher might be able to make something out of.