I had built a gantry crane at my old shop and really enjoyed it. Sold it to help make the mortgage when the economy turned down. Back to the industrial units, there are freestanding bridge cranes that would work great for the home shop. These come as preengineered kits. Yea, they're not as cheap as burning your own, but they're a heck of a lot safer. You can help the cost if you can be realistic with the hoist capacity and keep your spans down. Just Google "Freestanding Bridge Crane" and you'll get a bunch of hits.