The table top is Cabinet Grade Birch Plywood. It comes in 8' x 4' Sheets. I built a quater inch lip around the edge because the plexiglass sheet is exactly 8' x 4' also and will rest easily inside the lip.
The GRID..... I've had tons of emails about the grid so I'll post it here for all. (and on the website soon).
The Grid is drawn in PENCIL onto the table itself. With the table painted white, the pencil lines show up very clearly. I used a yard stick and a ruler to measure them and draw. It took about 15 minutes in total to make the entire grid. The benefit of pencil was that it is erasable if I should ever need to change scale or what have you.
Also with the grid being in the table I can lay over paper maps, (like those from dungeon magazine) be them square or Hex, under the plexiglass and they meld with the grid in the table to make the larger play area.
As far as being durable, I've never had to redraw the grid in over 2 years of having the table. So it's standing up well.
Plexiglass Top -- **VERY IMPORTANT**
To often folks confuse WET Erase Vs. DRY Erase. It's very important to remember plexiglass is a WET ERASE surface. Use a Vis A Vis marker to draw with. They are wet erase markers.
Do Not use Shapries or other dry erase markers.
With wet erase a simple spray of water and a cloth (paper towel) will wipe it clean.... And after a while if you notice sleight build up, you can just take the top outside and hose it off. =) Very practical and easy.