Most people's first project is a welding cart; I had to have a ball of extension cords and cables follow me around the shop for a couple years before creating one.

The biggest thing for me when creating one was power. When doing car work I normally have a couple grinders and an mbx blaster. Add in the plasma/mig/tig and it seemed a rats nest was inevitable.

Attached to the cart is a 30 ft 220v line which I use for the welders and split into 110v for the outlets. Metal outdoor outlet boxes seem to work well for mounting to a cart.

Here's what I ended up with. Hope this gives others some ideas.

I posted some more images here.