Itty Bitty Battlefields has a post on making 15mm trench systems on the cheap.
Modeling
Constructing A Native Village Tutorial
The Wargame Terrain blog has a nice tutorial on making a thatched hut native village.
Making Wargaming Hills
Here’s a nice tutorial on making insulation board hills for your wargaming table.
Sculpting A Chain Out Of “Brownstuff” Epoxy
The Excommunicate Traitors blog has a photo tutorial on making a chain out of the brownstuff epoxy putty.
Building A Cardboard Hill
Hills are among the most basic sort of terrain you need for a wargames table. Here’s some nice advice on building inexpensive cardboard hills.