what cage should I buy?
well, there are very many cages available and they can be very cheap, like 15 euro's or very expensive, like 200 euro's! I always advice to just look for a nice secondhand cages, they are cheaper and can be almost as new! But if you want a new cage, off course that will do to.
Mice are experts in escaping, so when you buy a cage make sure they are mouseproof! Bars can't be more then 0.8 cm apart! When you want a aquarium, also make a top! ( with good ventilation) And there shouldn't be any holes or easy the chew through places!
There are always several things to consider when choosing a cage, I allready noted the escape part, but also ventilation, draft, how many should go in there, what do you want in there (toys, houses), cleaning, weight and place to put it.
I will start with ventilation and work my way down this list. Ventilation is very important as mice are very active and they can also produce some smell, so you don't want a cage that doesn't ventilate and get's moist and smells! This isn't good for the mice and also not nice to have in your house.
Next point, draft... Mice are very sensitive to draft, the will get long infections when they are placed in a drafty invironment, so make sure there is no draft in a place where you place a cage when you have bars, when you are not sure, use a cage with plastic top or aquarium/terrarium, this way the draft doesn't go trough the cage.
How many mice do you have? If you have 2-3 mice a 60x30x30 cage should be big enough... when you have about 8 mice, I would advice something like 80x40x40. So before you buy your mice, think about how many you would like and buy a cage that is big enough for them. Because of ther curiosity and activity they will use the whole cage, they will also climb and dig if they can. What brings me to the next point of what you want in the cage! It's obvious that if you have a 60x30x30 cage you can't get as many thing in their as when you have a cage that is a meter long! If you want a whole playing ground with run wheels, climbing things, holes, houses etc, you should also have a bigger cage. Also to consider is how to fill the cage, in a cage with bars you can easily hang something on the bars, with a aquarium or terrarium this is a bit harder.
Now the cleaning part, the cages that are the easiest to clean is a labcage, but you can't really put much in their, so they you have a cage with bars or with a plastic cap, the one with the plastic cap, wich I use, are very easy to clean. The ones with bars are also quit easy, but once in a whil you will need to clean the bars too and those are not that easy. An aquarium or terrarium is my favorite as they are in all sizes and and they look pretty, but they are not always that easy to clean... when you have a big aquarium, you can't just pick it up and throw the filthy bedding in the trash, it's way too heavy! So with these I normally use a dustpan and sometimes the vacume cleaner for the edges and they also need a bath every now and then or you won't be able to see trough the class anymore.
I already noted weight in my point above, with cleaning it isn't very easy to have a heavy cage, but also if you have children that want to put the cage on the table to watch the mice and handle them.
And last, the place to put it, If you have a small corner where you wan't the mice, you can think about a cage that is a bit higher but not that broad. If you have a big side table, maybe a long aquarium or terrarium would be nice on there.