My opinion is that the story should be set in Castle Greyhawk, and should be focused on a party of adventurers searching the ruins for treasure. There should be one, or maybe two dragons. Care should be taken to differentiate this from "The Hobbit".
For example, the story might involve a group of regular folk whose lives are disrupted (lost job, house burned down, money stolen, etc.) and when a mysterious stranger at the tavern tells them there is treasure in nearby ruins for the taking, they decide to go get some of it.
Turns out the mysterious stranger works for a dragon (or is a dragon, in disguise) that is trying to steal the treasure of another dragon, and has been luring adventurers into the ruins for several months. This dragon kills the parties when they emerge and takes what they retrieved from the ruins. Our main characters are the latest dupes, but they slowly figure out what is going on, and eventually must escape back through the ruins while being chased by the dragon and its cronies. This might be the main part of the movie--escape. Play up that the dragon is a scary creature, sort of like the dinosaurs in "Jurassic Park" or the Xenomorph in "Alien". The characters have to decide at multiple points whether to give up treasure, or leave behind a companion, else be caught by the dragon. Their end game might be something like finagling the two dragons into a confrontation.