One crucial element of most cosplay, forgotten by most cosplayers (especially fat ones), is that you have to look like the character you're portraying, sometimes even without the costume.
Yeah... A fantastic costume won't really help if your weight, eyecolour (okay you can uses lenses), face traits are too different from the 'original' (as if, an anime character looked like a human being lol). Think of what it would look like if you cosplayed the character in pool/beach clothes.