Welcome! Great to have another Scot on here, there aren't many of us. Screen cages are much less common here than they are in the US, but many people still use them with success. I'm not a big fan of glass vivariums because they are size limited and expensive. My preference would be wooden vivariums because they retain heat better than glass and you can custom build them to virtually any size. If you decide to go down this route and don't want to build it yourself then you have a pet store near you called Proexotics that custom build vivariums. Psychobunny's suggestions were also good. Either way you want an enclosure with a mesh/screen top and lots of ventilation.
I'd recommend you read up on the forum before making your chameleon purchase, most pet stores will give you wrong information.