There are lots of options for making a great router table top. I bought one commercially that has a phenolic top when I had more money than time. But today I'd make it with sheets of Baltic Birch Ply (Apple Ply is similar. The BB ply comes in 60x60 inch squares, but I see it all the time in 30x60 sheets at Rockler. The key is to make sure it's flat. And for me that means buying it from a flat stack at a hardwood supplier.
I would cut two pieces to size, but with an extra 1/8th inch I could trim off later with a trim bit to give me a nice, clean edge.
I would buy the mounting plate (aluminum for me, not plastic), and use it to lay out the opening for the top piece. I'd cut the opening just inside the outline with a jig saw, and then and use the trim bit with boards for a template for the bit to run against for a very clean cut. Place several playing cards between the boards and plate for a good fit, but not too tight.. Use double stick tape to hold the boards in place. Like this:
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Next I'd position the top piece with the opening on the second layer and mark the opening on the second sheet. Make sure the two pieces are aligned before you mark the opening so they are easy to align when gluing them
Now make a second outline about half an inch inside the full size opening outline. This will give you a lip so your plate can't fall through. Cut this out with a jig saw (same with the top) then the trim router and wood guides.
Note that most router plates have curved corners. When you drill the holes to start the jig saw cut, do so with a bit that matches the radius of that curve. You want a snug, not tight fit so you can lift the plate and router out from time to time.
Next, with a nice, even coating of glue that you smooth out as flat as possible, put the two cut and inside trimmed pieces together. You now have about a 1.4 inch thick top. Connecting the two pieces is a little tricky because the glue will let them float, so you should find a way to clamp top edge to bottom, left edge to right so the pieces are as perfectly lined up as possible. I would predrill holes up through the bottom and use one inch or 1n1/4 screws to hold them in place while the glue sets. Do not place screws where you will later add T Track, or remove them after the glue is set.
Next comes laying out straight edges as guides for trimming the edges. You will be using a very long trim bit, so you don't want a lot of material outside the trim line. 1/8 th is enough proud.
Next for me would be applying a laminate top. There are lots of videos on how to do that, but the key is do not let the two surfaces touch and make sure the laminate is larger than the top. You will use a trim bit with a top mounted bearing, and the newly finished edge will be the guide for the bearing.
Once applied, that top will be water resistant. Be careful cutting out the center of the opening on top, You can drill up through the bottom opening so you can tell where the opening should be, and use a short top bearing trim bit to perfect the cut.
Laminate the bottom layer if you wish.
Edges. I'd leave the corners square so it's easy to add an edge of 3/4 hardwood. You can round off the corners of that edging. Tack and glue that edging, being careful that it is even with the top. You do not want it to form an edge that will catch your work pieces. That means you should make certain that edging is perfectly straight. Take time to plane it down until it's perfectly flat on one edge. Start with an oversized piece and once you have the straight edge, use a table saw to trim it to exact width.
Last item is leveling the plate with the top. You can do this with screws up through the corners of the under layer. Blunt the end of the screws. Or for about $20 you can buy a set of levelers by Kreg. Elegant solution.
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This is a fairly inexpensive build and you can have a top any size you want. If you don't want to build your own cabinet, make the top large enough to fit a commercial vanity with doors and drawers. My table is smaller but If I made one, I'd go with a 37 x 24 inches so it fit on a standard bathroom vanity case. But you could mount it on any kind of table or cabinet you can find. It will last your lifetime if you do it this way, and you can pass it on to someone else.
And it's really easy to add T Tracks and fences to your new creation.