|Models, left to right:|
H&R British BL 60pdr (WW1), GHQ A9 Cruiser (WW2), H&R Napoleonic Spanish artillery.
I've built some less rigidly geometrical terrain modules before: here, and here for example. I may return to that format, but I'll make a few of these hex-based ones and see how they compare in terms of playability.
I had a bunch of 50mm hexes I made many, many years ago from heavy 3mm thick card. Those were originally intended for a home-made copy of Knights of the Air (one of which, a Fokker D-II you can see to the left of frame), which did get completed but then hardly ever got played. I'll never use them again for their intended purpose, so waste not, want not. For WWI aerial gaming these days I use Canvas Eagles and 1/300 scale miniatures, mostly from Heroics & Ros.
I bevelled the edges of the card hexes on my belt sander. I was in two minds about doing that; on the plus side, it means that the hexes slope down to the table surface and will blend in better with a ground-cloth, but on the minus side, it makes them harder to pick up by the base to avoid damage to the terrain modeling.
The trees are very cheap Z-gauge railway scenery from China, some with plastic trunks, the others in twisted wire. I paid about $5 per 100 of the plastic ones, and if I recall correctly about $10 for a hundred of the wire ones. I mix the two, with the wire-trunked trees to the outside; they're stiffer and make it easier to pick up the hex, and they're a bit less regular than the plastic ones too.