My latest little terrain project was some Islands for Dystopian Wars, since using those old brown and white hills was too shocking, even by my standards.
The smart thing to do would have been to put down some ships for scale but the table they are on is 4'x3'. So there will be more room on the table than this picture suggests.
On of the pieces is a hardened air-base. I think the details need a little picking out but the main thing for terrain is to look right and be hard wearing.
Islands are polystyrene with Bostik 'Fill a Gap' as a coat to make them tougher. Since ships heaving in close to an Island always annoyed me in this game, I've modeled the shallows on some transparent blue plastic.The theory is that only small and medium models can touch the shallows - large/massive ones hit as 'Crunchy' (ie very bad) and take a lot of damage.
I've also done some sandbars/shallows. I think that the best way is to treat them as soft for collisions and let smalls and mediums cross over where it is blue.