I built a rack a few years back for a local wrecking yard to do the same thing. I used two lengths of 12 inch I beam for the wheels or hubs to sit in and welded 4 inch heavy wall sqaure tubing as legs and braces. I then fabbed up a sqaure pan to sit on the edges of the I beam to drain fluids into. The bottom of the pan had a fitting for a rubber hose to drain into a 45 gallon barrel. I forget what antifreeze was worth,but used oil went for 12 cents a liter. Then I had to repair the Cat loader and build a set of forks for it to move cars,but that is another story.