I spent two years trying to figure this out. I have a pair of water monitors I wanted to get outside. Not many people house monitors outside. It seems there are two strategies: A pit or a cage. If you can make the walls of a pit smooth enough, you don't need to top it off. I pondered building a wire pen and covering the top of the walls with metal sheeting on the inside. I also looked into industrial equipment cages. Definately strong enough and the price was not so bad. But, I worried about rust. I also considered using 1/2 by 3 inch aviary wire. This is available from several sources, and someone posted a pic here of their Argus in such a cage in CA. Doors are more the issue. I finally decided on a concrete slab with a custom cage on top. I ordered the cage from L bar M in CA. If you look on the Web, there are a few places building cages for exotics like monkeys and exotic cats. They are shipped as panels and you bolt them together.
When my drawn out research was done, I realized there were no good options that would not set you back about $2K. The cage I got is 12 by 12 by 6 and has two compartments for around that.
The slab was poured this morning, and the cage should arrive this week. Once the cage is set up and the lizards are in place I will post pics. If the lizards break out and terrorize the neighborhood, you'll see me on the news.
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Campti Sam