Big Thing

I want my feat next semester to be a really long movie. Like a ten to twenty minute, extremely plot driven, intense movie. I'd have to write it first. But I don't really know anything about writing long scripts. Are there somethings I have to know? Or should i just go for it. I feel like it's kinda like how a short story writer eventually wants to write a book. Do they need to know something else about writing longer pieces? Are there any tips you can give me? I'd really love to get this done.