Gantry Cranes

[Beaujolais]

I just wanted some help with making a model cargo bay gantry crane for a project.

I need some help designing the jib part of the crane. It only has to be a simple version and easy-ish to make.

I have the idea of bending sheet metal to form an L shape. Doing this twice would be my jib.
Then I would have the cart on it with motors to allow it to move and allow it to raise and lower a cargo container.

Sortof like this but simpler again:

http://img.nauticexpo.com/images_ne/photo-g/container-gantry-crane-ship-to-shore-189089.jpg

Anyway I just wanted to see if any of you guys have ideas of designing a cargo gantry cranes would be awfully helpful!
Any ideas at all will help me.

Thanks