I haven't seen this top before. But we could think this through together...
Measure your arms hanging by your side, wrist to wrist up and over the back of your neck, and then add an inche to that for the hem. Cut the square out. It looks like they took the tips off of the square to make the sleeve straight across. The neckline is just a little tricky. So use a scrap piece of muslin or tissue paper and cut it out with that first. It should be large enough to go over your head. Then measure how far down the neck should be in the front. When that is right, then tranfer it to the garment. Kind of like what you would do with a pancho neckline. Leaving an inch to double turned under as the hem. The neckline could be finished with 1/4 inch double fold bias made with your fashion fabric.
The sides are a square cut into fourths. Then sewn on to match the tip of the front V hemline and then up leaving a half inch at the end of the seam to match up the side seams. The sides are then sewn from the sleeve to bottom of the garment.
Then press under the hem all around, then again to make the raw edges enclosed and top stitch to finish.
I use a sewing form, so I do things like this often. And, I drape cut garments too. I hope this makes any sense. It looks pretty easy.
You can use a small pieces of paper (or fabric) to make a tiny one first. (Doll sized) That gives you an idea how it all should go together without cutting into your fashion fabric. Write down any thoughts or steps ahead of time on paper for your instructions.
I hope you can make heads or tails of my thoughts on this top. It looks cute and comfortable!