Let's be nice guys, he's new.
Broly isn't and will never be a proper character. However, you can download a Broly model to A) Replace one model in 1.2.3 (Usually Vegeta) or B) Use the custom model features in 1.3.
I warn you, there isn't a working Broly 1.3 model yet so if you want him, his animations may be messed up.