I was wondering which kind of exhibit you prefer, opentop or covered? This can be for any mammal like primates, cats etc. I know their have been some discussions like this in certain gallery's (can't remember which- I think the was one in a Twycross gallery).
I'm really not sure what you mean here... I can't see how anyone would vote for anything other than depends on the species. Open-topped may be fine for elephants but for un-clipped or pinioned birds, not so much... (seeing that you say mammals then the bird thing could apply to bats). Edit: I have just noticed something, you include neither on the poll... how can something be neither? Not open-topped but also not covered, what is it then?
It's hard to say really. Open topped looks nicer in my opinion, an is likely cheaper in many cases, but you have to consider containing the animals and looking after them. Some animals from forests are more comfortable being covered so they don't have full direct sunlight on them, and the bars on the roof can give primates more things to climb from. Generally, I'd favour open topped if we had infinite space and money. But we don't.