Depending on how big your grow room is I would suggest buying a HPS/MH conversion lighting fixture and bulbs, along with a good reflecting hood. If you want to harvest twice as often get two fixtures, separate the shed into 2 sections.
Get a metal halide bulb, 250 watts should be good to veg
Then get a HPS bulb, 250 would work but 600 watt would be better for flowering
Make sure the 2 areas are light proof and you can be harvesting every 8 weeks instead of every 3 months.