Many of us here have cages from here for our gtp. I love mine. I went with the 24/20 cage. It is 24 tall, 24 wide, and 20 deep. I choose it because it was preassembled, sealed, and the shipping was not terrible. It was really plug and play. My aru is about 4.5 feet and it suits him just fine he has plenty of room. You can also gets perches included. They are pvc and easily adjusted and removed for cleaning. I added a vine and another vine perch for extra climbing fun. He climbs around every night when he isn't digesting. He is fun to watch.
Usually it is recommended to have 2*2*2 cage for an adult but other here have the longer but shorter cages and say they really enjoy them. I'm sure they will chime in.
http://www.pvccages.com/new/
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