Here is the first draft of the most basic part of the table:

Notes on what you see:
-Different colors on similar parts denote slightly different dimensions.
-The black and brown pieces are 1x4 (actual dimensions .75 x 3.5).
-The green, white and purple parts are 1x2 (actual dimensions .75 x 1.5).
-Where 1x2s meet 1x4s, the 1x2 extends into a half-inch mortise in the 1x4.
-The 1x4s can actually be replaced with 1x6s or any other width of board.
-The yellow 4x4s (actual dimensions 3.5 x 3.5) are legs. They are obviously going to be longer than this.
-The red piece is 24x24 and represents a (probably) 1/8 hardboard-backed foam piece of modular terrain. Each sits on three pieces of 1x2 and/or 4x4, which sit half an inch below the top of the 1x4s. Panels can be lifted out of place from below when the terrain needs to be rearranged.
-The difference in height between supports and the 1x4 edge (here 1/2) is not final. In any case, the long pieces and the legs will share an upper plane.
Notes on what you don't see:
-The 1x4 walls may serve as the inner wall of a trench wrapped around all sides of the table. The trench would be used for units out of play, dice and so forth, or any other clutter we don't want on our beautiful OCD battleground.
-Further down the legs will be more supports, possibly a skirt and/or a plywood shelf, etc.
-Other possible features like foldout desk tops or drawers and shelves will occupy the space below the panel supports.
So again, this was the very first draft. It can totally be thrown out if it blows. We're probably going to come up with some new features we want that interfere with the placement of these parts, and that's ok.