I shared a post with a purple crop top in one of my monochromatic outfits and I was asked how I made the shirt. It is really very simple.
I had 2 school t shirts, one larger with shorter sleeves and one smaller with long sleeves in very similar colors. I cut off a band from the bottom about 12 cm in height. I then cut the shirt from the mid shoulder seam straight down to the bottom like this making it wider than the equivalent mid section of one of my t shirts.
I then cut the second shirt in the same manner and laid the long sleeved sections down next to the mid section of the other shirt. Making sure that the total width is wider than one of my t shirts as I wanted this to serve as a looser shirt which could also be worn as an additional top layer over something else.
I stitched the two seams on my serger. If you don't have a serger you can use a domestic machine with a zig zag stitch, if you don't have a zigzag stitch, sew 2 straight stitching lines very close to each other.
To finish the shirt off I added the band with the original hem from the larger shirt to the bottom section of the crop top.
I ended up with a loose 3/4 length sleeved t shirt that is very comfortable worn over other shirts or even as is in a color that I love.
The remnants and sleeves from the other shirt were used to make fabric flowers, yoyos and t shirt jewelry.