My son loves superheroes and when a family member gave him a shirt that was YEARS too big I immediately knew what I'd be doing with it. It took 3 minutes and is now proudly hanging in his room. The prized Matisse that I carried through Europe at 19 was shunned to the playroom to make room for this 6.99 tee shirt !
Here is what you do. You will need a staple gun, a teeshirt and a mounted canvas. Take the shirt with you when you buy the canvas. Now you can cut the tee shirt but I wanted to be able to at least send it to good will with only tiny holes in it when my son outgrows this stage so I didn't cut the tee shirt at all.
I slipped the canvas inside the shirt.
Start stapling with the corners, fold it like wrapping paper for a snug fit.
staple the rest.