http://www.empirecovers.com offers 3 different types of waterproof covers for your 2005 GZ250. They are: VIP Advanced Cover System, Titan 4L Motorcycle Cover, and Waterproof Motorcycle. Check them out, their prices are cheap and their covers are awesome!
Here is the link for the size cover needed for your specific model:
http://www.empirecovers.com/motorcyc...model=%20GZ250