Dang that looks so much fun :D
You have to get your hair to at least 20(in HK) or 25(in Taiwan)cm long before they can work on it. Mine is little more than 30cm I think(splitting my hair into 2 tails helps with cutting more hair and dealing with my naturally massive hair volume)?
I'm going to mail these to the cancer center very soon. Mom has one of those wigs made with human hair she got during her chemo and holy crap, that thing looks so real it's unsettling. I'm planning to do this again once my hair grows back to where it was :D