Well to tell you the truth, when I made my RPG, I made the Map Editor before the Engine. It seems like the logical thing to do seeing how it would be easier but i had to make a lot of corrections to the editor while doing the engine.

Basically, it is up to you. I created sort of a Temp. editor which I was going to imporve on later on. I put the basic elements like a Wall, Enemy and Death Spot on it so I can have something to work with.