Mascots are REALLY hard to do for your first time. When and doubt I would start with the body suite.
make some choices. do you want to look like you have fur or just have it like a plain spandex suite? If its the later you can buy it off the net more than likley. the first ones are harder to find and youll probably have to make your own.
I havent made a mascot before but I'm working on something like it.
there are a lot of tutorials and help online for mascots, I suggest posting on cosplay.com for help or searching google for tuts!
good luck : D