There are several brands of full-plastic-cages for small animals on the market. Some of them are
looking like "Space-Stations" - really good looking, but only to the owner - they´re all dangerous and should be avoided. Why ? Well, here´s
a list of known problems with these "cages", could be continued endless...
6 little holes of about 6mm are never enough to ventilate a cage ! Hamsters inside are living in a permanent "urine/ammoniac mist".
Please, don´t add more holes or make them bigger - in that case you´re only providing another point to attack for your hamster´s teeth ! If he can get his teeth on the plastic, he´ll chew himself to freedom ! The plastic is not hard enough for hamster-teeth !!!
Hamsters are living "by their nose". In a plastic-prison, they can´t get any scents from their environment. That´s the same like a human is imprisoned in a little cell without any windows. To feel secure, they need to "smell" their environment.
Regardless of what you use as bedding-material, your hamster will live permanent in an unnatural environment. Plastic-bottom, plastic-top, plastic-house, plastic-wheel, plastic-bowl, plastic-tubes..... . All he could chew on is plastic (even if you provide chewing-toys like wood-sticks, dog-bones etc, he will chew on his cage). And this plastic is not hard enough to survive hamster-teeth. If your hamster get parts of this plastic into his system, it will injure him inside (see health-section)
All known systems are insecure ! Hamsters CAN split them apart and get lose. Neither the plastic is hard enough to survive hamster-teeth, nor they´re made without any "attack-points" for the hamster. Hamsters are "escape-champions" - for sure, they´ll find a way if there´s any. And these plastic-stuff provides more than one point to start a try with good chances. See escape-stories in cage-section.
The wheels CAN come apart (esp. those outside the main cage-area) and provides another way to escape.
Hamsters are climbers - the love to climb - if there´s anything to climb on. In plastic-cages is nothing to climb on, only another plastic-thing. Normally, you should provide parts of trees inside your cage for your hamster to climb and chew on. Did you ever try to fix such thing inside a plastic-cage ? Forget it....
Well, this should be enough reasons to avoid full plastic cages.