Right now I have gone full redneck

I'd like to build a jig that sits outside, and has the ability to provide a completely flat and level frame surface, so that I can have the joints suspended for complete welding without needing to flip over a tacked frame, etc. I would like it to rotate on the horizontal plane to access all sides while all of the components are in place.
Does any such thing exist already, or do I have to start from scratch?
Joe