I would love a good old fashioned reptile house with multiple snake and lizard species, preferably some venomous snakes.
I feel the UK really lacks a really good reptile house. Cotswolds is nice, London is okay, but seems to be going the wrong way, and nowhere else seems that really committed in showcasing reptiles. I know Chester have a fair few bits scattered around and a lot off show, but I just wish someone would build a massive reptile house, with some cracking big vivs with exciting species and have some reptile walkthroughs as well.