Interestingly, a 120 cm x 120 cm enclosure has a floor space of 1.44 sq metres, while a 180 cm by 75 cm floor area is 1.35 sq metres. The difference is primarily in height - 60 cm high vs 90 cm high. However, I personally would prefer the longer, narrower shape as it is going to provide more accessible viewing of the occupants and allows for a better transitioning of the environment provided if you want to do a naturalistic décor. For example rock outcrop to sand dune.
I made some enquiries and there is no outlet in Perth that sells enclosures of that size. Nor are there any dedicated reptile enclosure builders. As I see it that basically leaves you with three options:
1. Go interstate. Buy from an interstate supplier of ready built enclosures of that size. If that size is not available, then contact an interstate custom builder of reptile enclosures. You will need to pay the freight of course so that needs to be figured into what it is going to cost you.
2. Keep an eye out on Gumtree and ebay for an appropriate sized enclosure.
3. Draw up a detailed design for the enclosure you want and get a local cabinet maker to build it for you.
I do know from personal experience that the last option is commonly used by herp keepers in Perth who are not into DIY and want something different from what’s commercially available. I’ve never enquired about what it cost them but I reckon it is safe to assume, utilising a decent trades person it is likely the cheapest option for a custom build.
Before you launch into anything, I strongly recommend that you locate a pair of ackies for sale and put down a holding deposit. There’s bugger all available for sale in WA at the moment.