Hello from London

Welcome. Building your own table is a good idea. Consider making it of two layers of Baltic Birch ply, One 18mm, the other about 12mm. Cut both to the same size for gluing together later. Get a mounting plate for the router and draw its outline on the top, thinner layer and cut that out. Lay this top over the bottom layer and draw lines 12mm smaller on each of the four sides, then cut that out. This will give you a 12mm recess for our router plate. You can use screws up through the 18mm lip to adjust the height of the plate to be flush with the top of the 12mm layer.

Be careful to find VERY FLAT ply for each piece. You can get fancy and put a layer of laminate on top, or just use pure paste wax on it and polish it nicely. Here's a drawing of the edge of the recess.



You can use a VERY FLAT board for a fence, or make something fancy, such as this drawing. Just make sure the face is 90 to the table. I also find a nice tall fence is nice to have. Sorry the drawing is imperial, not metric.