I started out with this basic square-cut grey animal-print t-shirt. It cost me $3 at an Anglicare opshop.
I removed the collar and the pocket, and trimmed the sleeves.
Then I added some random tucks to give it a bit of shape….
…. and topstitched them down in a contrasting colour (pink, but it didn’t really show all that much). Here’s a detail of the inside:
I am quite pleased with the fit, considering I didn’t use my dress form or try it on at all during the process!