picked them up yesterday. 1/2inch thick MDF squares.
only problem?
[the problem]
i got them from home depot, and the guy who cut up the 8x4ft sheet didn't actually measure, he just lined stuff up on very rough hand drawn lines on the cutter, so they aren't anywhere near uniform size.

i'd wanted 2ft by 2ft squares.. and i got that within about an inch either way.. i've gotten more accurate cuts from home depot before, i think the guy had just half assed it.

now i'll need to track down a guy from our church who has a real, fully equipped woodshop, see if he can trim them for me to be a bit more uniform. going to delay construction.

i also picked up some black, grey, and green spray paint..
my goal is to make something similar to this
i figure i can hit them with black paint, then use painter's tape to block out the roads, then spray them with grey to make the concrete areas where the buildings will go. buildings will be on separate bases, so i can store this whole assembly when it's not in use.
with 8 sections, i figure i can make 4 generic boards like the above (maybe with slightly different road layouts in the center), and 2 with some more unique layouts (though sharing the same 4 roads edge bits..thinking that parking lots and other such features might be fun)
the last two i'm hoping to make into 'parkland' boards.. instead of room for building's they have green open areas for hills and woods.
Buildings will be easy.. Burn In Designs and Gamecraft Miniatures both make fairly simple card, wood, and plastic building kits big enough to serve as mecha cover.. and have package deals where you can buy lots of them in bulk affordablely. though i'll probably look at some GHQ and other manufacturers farther down the line to add some variety.. it's just resin and metal is expensive.