If you're building a Rostock then a quality plywood jig is essential for accurate alignment. Have this cut from cardboard, acrylic, or wood. We like cardboard since it can be disposed of and you only need the jig once, really.
We converted the Rostock Delta Robot's Plywood Jig to SVG with some heaving lifting from the original files on Github. We went from SCAD -> STL -> DXF. Then we verified the units were correct in Adobe Illustrator. Illustrator is proprietary but it has some powerful SVG features. We created an Illustrator overlay of the jig so we could edit it and export to SVG.
This file is intended for a Ponoko P2 laser-cut template and generates multiple jigs, but it's still affordable enough for one person to make.