Several years ago, I asked if a ramp could be placed alongside the Pengin Pool, so children could see the penguins swim under water. "No, it's a listed building." What if the ramp were placed alongside the pool, so it didn't touch the building. "No, it's a listed building." It also seems that it couldn't be removed to an architectural museum.
I tend to think that new zoo buildings should be built using pre-fabricated materials, so they don't win architectural awards and can be altered simply and cheaply. Several older zoos seem to be lumbered with buildings that may have architectural merit, but are not suitable for animals. The Casson building wasn't good for elephants or their keepers and I don't think it looks much like elephants drinking at a waterhole.
When a new zoo exhibit costs more than a new school, something has gone badly wrong with the finances. One of my favourite zoo buildings was the old Rodent House in East Berlin. It was little more than a garden shed, but contained several species, such as gundis, short-tailed opossums, cururos and dassie rats. In fact, a zoo could have several such houses on the space being allocated for a new exhibit for big cats, great apes, elephants or other species, which are relatively common in zoos already. All you need is a new TV series that makes small mammals popular.