Crop tops are all about playing with proportions. So raise a cut when you're totally sure about it. Explore by using safety pins.
You can make a huge number of desired variations. Make a higher or lower neckline, crop your top with a side curve, give it a funky look, or make it oversized. Decorate your cropped top by drawing, spray painting a pattern, or simply writing on it. OMG! I think that's enough, I need to stop.