I honestly don't think a cage with a dome shaped top would be a problem at all. Its the ROUND cages you shouldn't get, as it confuses the bird, but a dome shaped cage pretty much is a square/rectangle...just with a dome on the top, so I do believe it would work just fine.

I have both a male and a female, and they are both wonderful in their own ways. Popcorn (male) is more outgoing and social. He's very naughty and goofy, and loves to hop around, sing, whistle, dance, etc. Very funny, entertaining bird. Muffin (female) is also very sweet. She's more a 'velcro birdie', and LOVES to cuddle and snuggle. Sometimes she falls asleep snuggled with my face. It is SO cute. She's more quiet, though she does get her 'moments' too, when she will scream.....BUT, that is rare, and only when she WANTS something. Once you give it to her, she quiets down. They both love to play with toys. Both love people...though Popcorn is friendly with anyone, and Muffin is more loyal/clingy to her family, and shy around strangers. I guess that should describe the difference between males and females...at least from my experience. In general, I believe tiels are more quiet compared to other birds of their size, and they have a lovely whistle too.

They're great birds. I would recommend getting two. Spend lots of time with them and they'll be friendly and tame, even if they have a companion. I got mine together and they both love people. I personally feel that every specie should have one of its own 'kind' to hang out with. Personally...I just feel that's something important for their emotional needs. Though many tiels DO live alone with people and do great, I just feel better that way. I wouldn't want to be cut off from human contact, so I feel the same when it comes to animals. Also, it helps that they have each other's company when I'm not around. A lonely bird is not a happy bird. They need constant 'friendship'. I'm not saying single birds are unhappy. If they have enough human contact, they do well, but I prefer that they have another tiel too.