All the TerrainLinx (TLX) sets and most of the others are designed to be unlimited modular sets - print and build as many as you need.
The modular sets are designed with pieces that fit together a bit like lego (in the case of TLX) or blocks (in the case of older sets) - combine them how you need at the time, and reuse them in whatever combination you want later. Don't have enough of something for your next layout, just print and build some more. - That's the beauty of the WWG PDF sets
Have a look through to the to see examples of what people have done with different WWG sets. (As a rule of thumb, examples based on 6"x6" tiles are generally TLX sets, examples based on 7"x7" tiles are using older sets.)