Well, I made one before, it was nothing more than 2 long pieces of uni-strut attached to an oak frame. Then I built a sled that held the router to ride on that. That provided the X -Y travel. I used Beeswax to lubricate it. It was a little clunky TBH, but it worked.
As soon as I get settled, I am going to basically to the same thing, but instead I am going to use slide rods with linear pillow blocks and affix to carry the sled left/right (X). Then on the sled, probably will build it and use it like before for the top bottom (Y). My rationale is that the slide on the X travel should be easy, but, the Y travel needs more resistance friction to travel since it is carrying a operational router. Thinking that will help make it more manageable. I attached the set of slide rods for reference, when I got them they were about 50 bucks. I think I got them off Ebay, might have been Aliexpress