I know what you mean about getting addicted to building enclosures.... I built 2, and then everywhere I went I'd see cupboards and tanks and bits of wood, and to everyone I saw my immediate thought was "How can I modify that and what could I put in there"....!!!
But then I thought about the other side of it.... "How can I afford to pay for the animals to put in them"..... So the cupboards stayed where they were......
I think my next venture will be an outdoor enclosure and either get a pair of Diamonds, or some Monitors.