I'm going to toot my own horn for a moment....
We've done
1) 1/16" G-10/FR4 Garolitem (2009, 2009 offseason, 2010, 2012)
Pros
-Looks darn good (glossy black)
-Very Stiff/strong
-Easy enough to drill, but vacuum the mess!
Cons
-Expensive
-Waterjet delaminates it, so they pierce 3-4" away from final cut and feed over. We did some external slots to act as rivet holes, then match drill rest on robot.
2) 6mm (~1/4") 5 ply baltic Birch (2012 offseason, 2013 season, 2014 offseason, 2015 season)
Pros
-Easy to cut
-Cheap
-Very HIGH stiffness to weight
-Can thread fasteners right into it for components
-When painted, looks nice enough.
Cons
-Termites
-Ignorant teams look down on it. This is fine, it just points out their lack of understanding of material properties and basic math
3) .125 6061-T6 diamond pattern (Waterjetted/lasercut). (2011 season, 2011 offseason, 2014 season)
Pros
-Hypetrain
-Forces you to do layout
Cons
-Expensive resource wise
-Not as stiff as the other 3 items
-One and done, no mods
4) .25 ABS (if you count 294). This is similar enough to (2007 season)
-It's really just a heaver version of plywood. I'd use plywood over this.
I highly recommend the wood, no need to laminate or do anything to it. Just use it as is. If your frail ego can't handle the wood, garolite is a great option at 1/16" thick but requires more tools to work with.
The diamond bellypan is nice... but in nearly all cases is a huge resource waste. Many subsystem gearboxes and gussets could be cut in the same time.