Need some advice.

[ClayPigeon]

Before even starting to make stories, I'd advice you to start mapping some rooms, houses and different environments from different categories(Outdoors, underground, caves, mountains, indoors, rooms, prisons and so on), to practice on your mapping and best it. (These maps won't be in your story)
I mean, just perfect your mapping skills, so they'll be good enough for your story.
Then, after your skills are good enough and you can map pretty well, and light rooms accordingly, you can start thinking of a plot for your story. Don't make it too childish or corny, but don't make it too dull or un-scaryish as well.
Make it interesting and worth playing and make it reasonable, everything that happens has a reason.
After you've thought about your story, you can start mapping for your story.

After finishing the first map, you need to start scripting it IF it has any events in it. (E.G: A monster appears, a sound plays, a key unlocks a door).