Everyone's dirt is different but the one time I tried to build ridges before I planted it did not work well.  We built them in the fall after we had disked the field and they looked great.  We were excited.  When it was time to plant on them 6 months later they were not firm.  It was a much different seed bed than flat, disked ground as the ridges wanted to blow out on some rows.  Maybe the guys who plant on beds down south will chime in with how they do it.