I just completed a router lift. My plunge router has an irregular profile, so creating a cradle for it was frustrating. I gave up on designs that are built around a model similar to the one Joat posted. I bought a couple of heavy-duty ball-bearing drawer slides. These could be held to the router using small bolts through the handle-mounting holes (I obviously removed the handles). Using wooden shims and some sheet-metal strips, I created a way of sandwiching the lower (when inverted) end of the router so the axis of the bit would be held parallel to the movement of the slide. Then I built a frame with couple of wooden supports to attach the outer parts of the slide perpendicular to the underside of the table. This allows me to remove the entire mounting plate to change bits so there's plenty of room.
The device lifts using a 1/2" threaded rod with a nut embedded in a piece of wood attached to the router-slide assembly. That is turned by a crank assembly salvaged from a seed-spreader a friend was throwing out. the crank axis is 90 degrees to the axis of the threaded rod. This is mounted on a "floor" made of a wider piece of plywood held by the frame. The whole thing looks ugly, but works great, and since the gear ratio allows the bit to rise 1" for a complete revolution of the crank, adjustment is a breeze. The whole thing cost under $20, since the spreader was free.