In general, the crate should be plastic, with metal bars covering ventilation windows on the sides and back and a metal grating door that securely closes. It should be big enough for the dog to stand up and turn around in, but not much roomier and properly ventilated. Too big and the pet can get tossed around in turbulance and injured, too small and you risk circulation and other problems. Asking your vet regarding size is really the best route. Actually, we directed all questions about shipping our pets to our vet. Even though a re-lo company can provide some good advice its really best to have a discussion with your vet about what to do and expect. You can also ask the re-lo company about crate sizes, as lots of them have a chart to use as a guide (even if you aren't using them to supply the crate) and/or ask makers of the crates. Generally, the staff at a pets mart/ pet co. will be able to tell you if a particular crate is airline approved. Call the cargo department of the airline you are using for the specs of an airline approved crate if you are unsure. Some airlines also list info on their web sites. Also spend some time finding/ testing proper water bottles that don't leak quickly. Buy two, and freeze the water in one and put fresh water in the other. Find a good, absorbant pad or litter (that your dog won't eat/ choke on if it chews everything) for the crate. Ideally, you should have the crate several weeks or more before shipping to get the dog used to it (especially if it isn't already crate trained) or being shoved in there for the first time for upwards of 12 hours can be traumatic.