when i make a map i always do a few things
1. i come up with what type of map i want, be it urban, industrial or what ever
2. I think of what kind of props i need and which set has the most props for my idea (city, indust. historic. ghetto)
3 i lay my idea on paper in crude drawings with all my buildings layed out in the area i want them.
4. i make my map
5 sometime or i should say most of the time you have to tweak your design. no matter how much you think about it something even little things will make you change something in your design.
hope that helps thats what i do when i make a map for any game.