Use Susy in your prototyping tool? Here's a stupid simple Sass mixin for easy content column layouts. just include it and go!

Susy grid classes mixin

@for $i from 1 through $total-columns {
  .col__#{$total-columns}-#{$i} {
    // Mobile & Tablet: on small and medium screens, all columns are full width
    @include span-columns($total-columns);
    // Desktop: when no longer on a medium display, obey column sizes
    @include respond-to($medium) {
      @include span-columns($i);
    }
  }
  
  .col__#{$total-columns} {
    @include container($total-columns);
    @include respond-to($medium) {
      .col-right {
        @include omega;
      }
    }
  }
}

/** MARKUP EXAMPLE
 * div.col__12 > div.col__12-7 + div.col__12-5.col-right
 */