Handmade Harry Potter shirts help?

As most fans (and pretty much everyone else) knows, the last Harry
Potter film is coming out next week. I'm going to the midnight
premiere and I wanted to make a shirt. My funds are lacking, so all I
have are the basic things: a plain shirt and some paints and such.

What I would like some advice on is this: my handmade shirts usually
look like crap partly because I have horrible handwriting and partly
because I don't have any creative ideas. Basically, any advice on how
to ensure that it doesn't look like a five year old made it? And
creative ideas? Anything is welcome!

Thanks!