The present disclosure relates more particularly to kits and systems of roofing shingles that can provide a variety of shingle coverage thicknesses and patterns while simplifying design and installation. In one aspect, the disclosure provides a roofing system comprising a first array of overlapping first shingles disposed on a roof. The system includes a first number, n>=2, of overlapping horizontally-extending courses of linearly arranged first shingles, with horizontal and vertical offsets between courses. Each first shingle includes a top headlap portion extending from the first lateral edge to the second lateral edge and a bottom tab portion formed of a plurality of tabs extending from the headlap portion toward the bottom edge of the first shingle, the bottom tab portion having an open area that is at least 20% of the total area of the bottom tab portion.