I suppose if I’d have wanted to be super fancy I would have made the t-shirt from scratch too but I just bought a pre-made one to experiment with and went to town with some dino printing. I bought some thin foam sheets that cost about 50p each from Hobbycraft (I loves me some hobbycraft!) and drew a stegosaurus onto it.
I should point out I like dinosaurs, and was really indulging in dino love at this time of my life (I have dino stickers, posters, hair grips, fabric, cards, temporary tattoos, ornaments). But thinking practically the image for printing had to have a simple and recognisable outline as any detail would be lost. So a stegosaurus was the obvious choice.
I bought some Dylon fabric paint and painted it on to the foam stegs then printed them on to the t-shirt, but the foam didn’t transfer very well and I had to paint over them with a paintbrush and I ended up using a whole little pot of paint and I only painted them on one side of the t-shirt.