No matter what scale you wargame the Vietnam War in, you're going to HAVE to have a whole lot of rice paddies. Buying pre-made wargames terrain is generally ridiculously expensive, so I've taken to building my own paddies. Here's how I go about it:
Let's do just a simple, ground-level, rectangular paddy. The first thing we need is some sheet styrene.
Thick enough not to warp or bow with a little weight on it. I think this is 0.60". Cut out a rectangle big enough for the scale you game in. Remember, paddies come in all sizes, from extremely large to very small.
Next, we need to build retaining walls. More like berms, really. I find the scraps from styrofoam Terrain Maker hexes are perfect.
Cut straight berms, ideally they'll be sloped on both faces, long enough to enclose your styrene base and then glue them to the base.
The berms sit on the base itself, at the very edges. Then add an internal berm or two, so it's not a single paddy. I use Woodland Scenics Foam Putty to plaster all the cracks and fill in any gaps I left where the berms should join. After all that's dry, paint the whole thing, inside and out with Flex Paste. This thing needs to be watertight for real!! Trust me, you'll see. Keep reading.
Next, paint the berms in whatever color you've selected as your soil. I use terracotta. Superglue a couple of painted civilians and a water buffalo or two onto the paddy floor (in 1/285, in this case). Paint the floor of each paddy section a slate color. I use Woodland Scenics Water Undercoat. Now's the time to glue the odd bush here and there along the inner walls of the berms.
The next thing we need is some "water". There are a number of products available, so use whichever you like. I use Realistic Water by Woodland Scenics.
It's important to fill the paddies no more than 1/8", allowing 24 hrs to dry. If you pour in too much, it'll crack as it dries, as well as submerging your civilians. Pour a bit in a small cup and add a bit of light brown paint to make a tea-colored mixture. It needn't be your soil color, as the water in paddies is often a different shade than the surrounding ground. You should vary the shade of your "water" each time you make a new paddy. That's how I remember the real ones looking. No two the same color.
You can string together groups of these into any shape or size you want. If you try making them too small, the "water", which contracts as it dries, tends to warp even thick styrene, so it's best to stick to making larger paddies and just subdivide them internally. I don't try to add sprouting rice, as it just never looks realistic. A fully grown crop would be easy; just leave out the water and villagers and deeply fill the paddies with a verdant green flock or static grass. Now glue a few bushes along the outer walls of the berms and you're done.
That's it! Quick, easy, and a whole lot cheaper than buying them.