best material to build a router table top ?

[manutd]

Decide how often you will need it. if you use it a lot spend the money and buy or make a good one.
If it is for occasional use, buy or make a cheap one. There are hundreds of examples on You Tube.

[manutd]

You need to ask yourself three questions.
1 - How often will I use the router table?
2 - What will I use it for?
3 - How much do I want to spend?

The answers should help you decide what you want/need.