If you have no waterjet or laser access we have used this engraving tool to trace the edges of the part from a drawing to transfer it to the surface of the metal:
http://www.homedepot.com/p/Dremel-12...0-01/100394725
It works well if you place a drawing onto the metal sheet and trace around it or make a straightedge with a piece of scrap. Takes a minute or so to trace the outline and it is usually accurate enough to make one to scale properly. We learned our lesson last year and match drill everything that is not the proper gusset from VexPro. We line up one hole, stick a rivet in with the gun, and then drill the rest of the pattern.