Personally, I do not like to begin with mapping all shapes, as there's always places I don't think fits to the places I've mapped afterwards.
I just like to take piece by piece and always zoom far away to see if everything fits together.
And zoom very close to see how it fits for "in-game" view.
Just a suggestion, but you could make a step-by-step tutorial for how to map most efficiently and convenient.
I don't know (but doesn't suprise if so) if any other people do it this way, but I like to first begin with:
1.) Have an image in my head of how it can be ("planning")
2.) Start out with walls and all shapes (but bit by bit, room by room)
3.) Add wall details and ground borders
4.) Adding ground details
5.) Lastly, add ground textures
Note: Not supposed to be a tutorial, just a quick in-depth on my way of mapping.
Tips for landscapes:
Never have only one flat floor, try to give a great overview to lower and higher floors.
Makes a greater atmosphere.
//Munchie.