They have the same cage-style of design at Port Lymne. Folllowing public complaints, they added the large outdoor areas as unlike at Howletts they had the space to do so. But outside of the scatter feeds the gorillas rarely use them, mainly they just stay empty throughout the day. Gorillas like cover over them.
I guess it seems strange that London is currently doing a big redevelopment when presumably just building a big old cage is cheaper than trying to make something open etc.
I mean, I'm not someone for whom great apes hold a great deal of appeal anyway!