We are planning on making it about 20' long and 7' high and having it involve a number of vertical members that can be moved along the 20' length. the pipe could then be clamped horizontally to the verticals at what ever spot is needed for a particular gate size. It will work best if the jig or rack stands fairly upright and all of the members are adjustable in both horizontal and vertical directions.
I know that there are jigs like this out there, I've just never seen one. Any help would be appreciated!!