Do you have approval for this from GW?
There have been several attempts at a fan-made movie based on GW IP and I dont think that any have ended well. In a couple of cases, a lot of money was spent on a movie that was never able to be released (Bloodquest).
The only actual release was one that was licensed from the start (although your opinion on whether this was a success or not depends on how much you like the movie!).