Router tabletops are almost a necessity if you use any of the large profile router bits that are available. If you currently do not use a router table, you will eventually need one. You can build your own router tabletop or buy an expensive one. A homemade, DIY router tabletop will save you money, however, and you can customize it for your specific needs.
The first thing you need to decide is how you will use your router table. Can you leave the router table set up or does it need to fold up for storage? If you have limited space, a fold-up version would probably be a wise decision. A permanent router table is more stable but also requires more space.
Router Tabletop Material Options
Decide on the size and material you will use for the top. You can choose between a plywood base with a laminate top, or an MDF (Medium Density Fiberboard) top. Both of these options need to be wrapped with a hardwood for protection and stability of the top. Use two layers of the tabletop material for stability and to keep the top from sagging over time due to the weight of the router and its base.
Router and Router Plate Options
Choose the router and router plate for your top. You need at least a 2 hp router, and would be better off with a 3 hp model or larger if you plan on using any of the large profile bits that are available today.
Once you pick your router, you can then decide on the router plate. There are a few options to consider in how to change the router bits. Can you access the bit from above or below the tabletop, and can you adjust the bit height from above or below the router tabletop?
Finally, you need to decide what you will be using the router table for. If you plan on using it to make mostly moldings and edge work, then it should be placed toward the front of the table. However, if you plan on milling large panels that need support, then you should place the router and router plate toward the rear of the table. With that in mind you could place it in the middle to do both and add a miter track in the tabletop.