Usually Wii U games don’t require you to have a mandatory install. Well it looks like you will have to do an install for The Legend of Zelda: Breath of the Wild on Wii U.
As posted on the official Nintendo website, you will need at least 3GB of storage on the Wii U’s hard drive or USB storage device to install The Legend of Zelda: Breath of the Wild. This is of course if you plan on buying the physical copy.
If you are buying the Wii U version of the game digitally, you obviously need more space as the entire game takes up 13 GB of data.
Make sure you have enough space on your Wii U before you intend to buy the game. 32 GB Wii U owners may not have to worry but those with an 8 GB model may have to find additional storage.