This striped sweater is worked top down, using a simple pattern (garter rib). The raglan yoke is worked flat for the most part, then continued in rounds. After dividing for body and sleeves, continue in rounds (or flat, if you prefer). Finally, stitches are picked up from the yoke opening (along a raglan line) and a button band is worked in rib stitch. This button band is closed with 4 buttons. In this sample, another button band is worked along the opposite, closed raglan line.
Even though the pattern is simple, some experience will be helpful.

This sample uses 6 colors, but it can also be made from one color, or 2, 3, …, or by working broader/finer stripes.