Oh my golly...I LOVE this shirt I made. I bought a pink t-shirt from Walmart for $4ish. It was in the craft area. There were lots of colors and sizes. I bought this to be a night shirt so I wanted a big t-shirt. You could even buy one of the $.99 plain shirts at Goodwill.
Start with a plain shirt.
I opened a Word file and just typed in what I wanted the shirt to say and chose the font and size. I printed it out and then used a Sharpie marker to trace it so it was a bit more bold. You could just print it out filled in.
I put the paper under the shirt and could see it enough to use a fabric market to trace it.