Here are some more great links to look at. My advice when making a map is have an idea of what you want. Like teh titanic or castillo. Ricks idea was a large ship and mine was a remake of a SOF map called Jordan. Maps like snowmen are theme maps and have no set direction of what they will look like. Theme maps can get out of hand for size. Make prefabs. Some examples of prefabs would be a house in my snowman map all the snowmen sences are prefabs the rinks are the slide is. What great about prefabs is there small and you just drop them into you terain (map). It makes thing very easy to manage.
http://wiki.modsrepository.com/index.php/Category:Mapping
http://iwnation.com/forums/