Another way to flesh out a level before designing it is to roleplay through it. In the simplest manner, you can just pretend you’re the player going through your level. Try to think of ways you can cheat to get out of overcoming all of the obstacles in your path. Think of all the questions you might ask yourself about the level as you’re playing.
The advanced method is to use an actual pen-and-paper roleplaying game (RPG) and run some friends through your level. You’ll want to use a flexible RPG whose player characters have abilities roughly equal to those in your game. The advantages of this method are that it reveals a ton of weaknesses in your plans, gives you a lot more ideas to implement, and really firms up your concept of what your level is all about. On the downside, it’s a lot of work, and you won’t get as much out of it if you’re inexperienced at running these sorts of games.
Beginning Game Level Design John Feil i Marc Scattergood