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.
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.
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.
That's it! Quick, easy, and a whole lot cheaper than buying them.