PLANNING YOUR TABLE

The very first thing you should do when you set out to build wargames terrain is plan your table. BY this I do not mean go forth with ruler, calculator, set square and pencil, and draw up a complicated diagram of exactly how to construct the perfect games table (although you can do that). No, I mean decide on the type of terrain your table will be composed of. You need to decide what sort of ground to use, and what sort of features will be involved.
There are several factors which will be involved in this decision. First: Which game do you play? If you play warhammer fantasy, there is no point in building an entire necron tomb complex, or a tyranid infested sewer system. Likewise, if you play 40K, you may not want to use the traditional 'rolling green fields' table. The army you use is also important. If it's your personal collection, why not make it fit your personal army? So, for instance, if you play Tomb Kings, you can make desert terrain, or if your a cold blooded Lustrian, make a jungle. Another consideration is how versatile you want the terrain to be. Are you happy always playing on the same sort of table? Or do you want to have the ability to use different features to transform your table to a completely different setting?
Here are a few things to consider at this point: Any 'specialty' table (i.e.: Snow, Desert, Urban) will be difficult to adapt to any other use. This is fine if you are at a club, where there are several terrain sets (HGC has Desert, Wastelands, Jungle, and Rolling Fields, all of which can be used in both WFB and 40K, and altered to represent different locations). However, if it's your personal set, you might not have space, or the time, to build several complete sets. In this case, I recommend you stick with the 'rolling green fields' sort of table. The simple reason for this is that with a grass base, you can adapt to several types of terrain. You can have rolling fields, or jungles, farm lands, villages, elven realms and more, simply by altering the look of the features. After all, the difference between the Empire and BRetonnia is only architectural.
The next question, is how will you represent the ground? Will you use a cloth, will you model it onto the table, or will it be modular? All of these have advantages and disadvantages. Cloth is the easiest to store, since you can just roll it up. You can also make hills under the cloth using books, boxes and other junk. However, cloths are never the most realistic of table coverings. Modeling the entire table looks very good, but it can be annoying to store. Or it can be impossible if you play on the dining table (like me!). Modular terrain is the ideal compromise. You build several large panels, and model the ground onto them. You then place them next to each other on the table top, and away you go. Modular terrain has an added advantage, in that you can model features into the boards, such as rivers and gullies which can;t be represented realistically any other way.
Once you know how the ground will be represented, it's time to decide what will go in the collection. You only really need a rough idea, as you will inevitably think of other great stuff later on. However, it's good to have a bit of a plan to work to. It will help define the look of your terrain collection, as well as giving it a geographical focus. You might decide, for instance, to have an Empire terrain set, or one set on Mars. For an empire set, you need plenty of buildings to represent farms and villages, as well as watch towers, rivers, fences for field boundaries, hills and woods. For a Mars set, you need a lot of red stuff. Also, you need as much mechanical stuff as possible, considering Mars is the home world of the Adeptus Mechanicus.
A really good way to decide this sort of thing is to look at the terrain tables in the Rule books. Warhammer gives you seven different lists, covering the entire old world (with the exception of Cathay, which in my opinion could use the Empire list, with different architecture)
Probably the best place to start would be to take the list, and make one of everything on it. As an example, let's follow my planning of the Khemrian terrain set for HGC. The Khemri list is as follows:

1. A deep ravine
2. A wadi
3. Boulders
4. A Jebel
5. A sand dune
6. Palm grove or scrub
7. A Ruin
8. Group of buildings
9. Oasis
10. Quicksand

The first thing I did was to decide which of these features to build. Some, like the Ravine or Wadi don't look good unless you're using modular terrain, so they where out. Also, quick sand is very difficult to model, and rather annoying in game terms, so it was out as well.
Next, I decided how many of each feature to build, and added a few items which aren't on the list. The resultant list can be found below:

1. Boulders: at least four bases
2. Jebel: at least one
3. Dunes: two or three
4. Palm groves: three to six
5. Buildings/ruins: two or three
6. Oasis: one
7. Crags/rock piles: at least three
8. Columns: two or three
9. Obelisk: one
10. Craters: three
11. Temple: one

As you can see, this is a fairly long list. But consider this: I designed this terrain set to be compatible with both 40K and WFB, and to cover two entire 6X4 tables. You can make do with less than half this. (The first time we used this terrain, only the boulders, two palm groves, the jebel, one dune and a building where finished, and it was just right for Warhammer.)
Of course, you'll come up with other ideas, or change things round. For instance, I have decided that more dunes would be a good idea. I also decided to make a crashed doom diver for this set, since the other one is so popular.

Now that you know roughly what your terrain set will be like, it's time to get working! Happy building!