I've had a number of people ask me to explain the process I use for creating maps for Dungeons & Dragons using Adobe Illustrator. Here is a very basic tutorial to get you started. You might want to get the Old School Hatching texture I have on DriveThruRPG or make and scan your own hatching as a background for your map.
Due to all the images I've created this as one large image. Click below to see at full size.