In the introduction, describe to the Heroes why they are undertaking this quest, to find a treasure, rescue a damsel, defeat an evil warlock, etc.
When designing the dungeon, think about how you want the Heroes to move through it, what they will encounter and how difficult it will be. If your evil warlock requires a special artifact to be defeated make sure you include that in the dungeon.
You may want to create a unique character the Heroes must defeat at the end of the quest. Remember these characters can also use Chaos Spells.
Once you have made these decisions you can start creating the quest pages needed to allow others to play.