Over recent years, there has been a tremendous and rapid progress in power scaling Yb-doped fiber-based picosecond sources due to their high efficiency, excellent beam quality and immunity to thermo-optical effects. These remarkable properties are not only very attractive for many scientific and industrial applications but also for frequency doubling to generate green. Besides good beam quality, a high degree of polarization and a narrow linewidth, further increase in conversion efficiency requires high peak power and increased crystal length. High peak power can be obtained by employing a fiber master-oscillator power amplifier design (MOPA) where seed pulses with adequate duty cycle are amplified to high average powers. However in this arrangement minimizing nonlinear effects arising in the fiber amplifiers becomes a challenge. The amplification of picosecond pulses causes linewidth broadening and the spectral bandwidth of the crystal is reduced by a preferred longer length. This trade-off can result in lower frequency doubling efficiency. In this paper, as well as the benefits and limitations of fiber lasers applied to nonlinear frequency conversion, we will review the various design considerations for the development of a high average power picosecond green laser based on single-pass frequency doubling of a fiber MOPA system.