When we first started the Makerspace, before we had even rented a building, we talked about having members build rolling carts that would serve as portable bench space with personal storage underneath, and which could be rolled out of the way when they weren't being used. We ended up using pallet racks for storage, and a random collection of tables and benches for work space. But I always liked the cart idea.
You don't want the cart rolling around while you're working, and I didn't want separate toe brakes on each wheel. After looking at several possibilities, I ran across this page, with a nice solution to a similar problem: http://www.woodgears.ca/mobile_base/table_saw.html
When you pull the handle, the wedges lift the table onto the wheels. The metal strips on top of the wedges keep the bearings from digging into the wood. After I took these pictures, I made different wedges with a steeper angle (30 degrees instead of 15), because our floors aren't level and I needed it to lift up higher. I also replaced the temporary handle shown here with a longer one.