How did you attach the rack to the roof? It looks like you attached it directly to the factory side rails, right?
Of what I've read, the max stock capacity of that rack is 200lbs. I don't know if this is purely due to the stock flimsy cross-bars, or the way the rack is bolted to the roof reinforcements only in a few places.
Most often, heavy racks are attached via gutter mounts and aftermarket cross-bars (like Yakima, or Thule).
I think the rack you built looks great, and functional. Just be aware of its weight, and the potentially limited load carrying capacity.