In addition to the Round House, the Anteater Lawn, Penguin Pool and North Bank Aviaries are also vacant, although the latter will almost certainly be demolished due to their small size (and of course the Penguin Pool is a whole other matter).
There’s also a spattering of other enclosures that are disused parts of a much larger whole. Main ones that come to mind is part of an indoor section from the New Lion Terraces, the small Duiker/Antelope paddock at the Lion entrance, the vacant side cages from the Insect House, and the fake mountains on the Mappins (which are practically one enclosure in their own right, they’re just too inaccessible to current paths and too unsuited/old to house anything, even with some modern augmentation).
There’s also others that I think are being used for storage at this point, or ones like the Ravens’ Cage that are purely ornamental (or the Llama House, which is now the First Aid area).