I work in the small animal and fish department at a pet store, and while I’m not an expert, I would like to at least offer my opinion and rebut some things mentioned previously.
First, the typical “hamster cages” you find at a place like Petco are generally unsuitable for most small animals. You want A MINIMUM of 360 square inches of floor space for the animal to be completely happy; too small of a cage is the #1 reason for bites. 9 times out of 10, when I deal with a customer with an “aggressive hamster who bites/nibbles”, the floor space of their cage is less than 360 square inches. For this reason, I do not recommend the overpriced plastic wire cages. They’re too small, they’re expensive, and the wheels that most come with are best equipped for Robo dwarf hamsters. Some have larger wheels, though most do not. Ones made by Crittertrail (a very popular brand) are also notoriously easy for the animal to escape from. I will not sell one made by this company to a family with cats for this reason. Better safe than sorry.
I am a huge supporter of aquariums or plastic cages. A 20 gallon long tank will run you (at most) about $30 new, or you can find them used for much less. They have over 400 inches of floor space. So long as you use a wire mesh top (either purchased or made), I have never heard of a hamster having respiratory problems. You do have to ensure bedding changes are performed on time, but the same can be said about performing changes in wire cages as well. With animals that have more ammonia in their urine (like mice and rats), I do not recommend them. But hamsters are fine. If the animal is a dwarf, go no longer than 14 days between bedding changes for a 20 gallon long. Aim for every 7 days; 14 would be maximum. For a Syrian, you would want to perform them more often.
If you get the glass aquarium with the wire mesh top, DEFINITELY get a lock. If you can’t find an aquarium, pick up a cheap plastic Rubbermaid container from Walmart and make a cage out of it. Measure the floor space of the bin to ensure it is at least 360 square inches. You will have to cut the center of the lid and put wire mesh over it for ventilation, as well as lock the sides, but they are excellent for the hamster owner on a budget.
Another reason people may have had issues with “ammonia buildup” in glass aquariums may have been due to the bedding used. Aspen is the only safe wood-chip type bedding for hamsters if you are going for the wood; when pine and cedar mix with rodent urine, it releases a fume that can be toxic. Go with paper-based if you can, but if you like wood, aspen would be your choice. 🙂
Is it a Syrian or a dwarf hamster? If dwarf, is it a Russian, Robo, Winter White, or Chinese? All these different species have different needs, especially in terms of diet. And their temperaments and needs vary widely as well!