This is actually a short sleeve top I made almost two years ago (!), I just drafted the pattern using a t-shirt I already owned and, instead of cutting the body of the top at the sleeve point, I continued the shoulder line, perpendicular to the neck line. I explained how to create the flare, in the How to make a flared waist tank top blogpost.
The construction is very simple: I first sewed the shoulders seams together, then the side seams. I then finished the flutter sleeves, the neckline and the bottom hem. Very simple and very practical.
Sewing pattern: self-made. Similar to this one I described here.
Things I wish I’d done differently: Maybe use a more drapey knit?
Fabric: 1.1 meters tie-dye knit I bought in Barcelona for maybe a couple of euros.
No notions, thread from my stash.
Final cost = a couple of euros 🙂