Actually, and not to be the annoying know it all here, but a Habitrial Ovo is way too small for a syrian (teddy bear) hamster. The tubes are too small and the whole set up is just plain cramped for them.
The absolute minimum sized cage a syrian should be housed in is that with a 30 inch by 16 inch floor base, though bigger is obviously better. I have my syrian in a 29 gallon tank. Yes, I know its a little smaller than what I recommended but its what I had on hand and its way better than cramming a poor syrian hamster into a ten gallon tank, or worse, a store bought hamster cage.
Tanks are just fine as a cage for hamsters, ventilation is not a problem with them as long as one regularly cleans it out, with spot cleans in between times. I clean ever 1 to 2 weeks and have no problem with ventilation. The absolute minimum tank size a hamster of any kind should be kept in is a 20L. Remember, floor space is everything. 10 gallons should only be used for betta fish, and not hamsters, its way to tiny for a hamster, even a dwarf, as they are extremely active and need more space. Especially a pair.
A dwarf might be fine in a store bought cage with extra additions but they are very active and like to run around a lot, so the larger the better is obviously the case here. Also, get two of everything in their cage, if keeping a pair, and an extra cage/tank so you can separate them if they begin to fight.
Something I've noticed that hasn't been mentioned here is diabetes. Dwarfs, like Winter Whites and Chinese hamsters are highly prone to that so a diet low in sugar as possible is an absolute must. I highly recommend feeding Hazel Hamster food as its the best out there. Don't feed them any fruits, berries and make sure to absolutely minimize the amount of carrots you feed them. Also, go and buy diabetes test strips to test the dwarf's urine for diabetes so you know if they might already have it and can adjust their diet accordingly.
Also, don't ever use a wire mesh wheel. Use a solid plastic wheel and make sure that its at least 6 inches big in diameter. The smaller wheels aren't useful to any animal and should not be sold IMO.
NEVER EVER EVER keep a female with a male unless you are an experienced hamster breeder, know absolutely 100% about every genetic and behavioral trait a hamster could possibly get and know 100% that your dwarfs aren't hybrids, which coming from a pet store, they most likely are. In which case, being from a pet store, they should be housed separately. NEVER EVER EVER breed pet store hamsters because you have absolutely no clue about their genetic history and their lineage.
I highly recommend keeping a same sex pair.
Last edited by TheCrabbyTabby; 08-09-2012 at 08:36 PM.