Heidi Montag says she's tired of being a reality show star -- and now that "The Hills" is ending next season, she can't wait to finally become "a full-time motion picture actress."

Heidi Montag
Montag -- who recently starred in a FunnyOrDie sketch and makes an appearance in Adam Sandler's upcoming movie "Just Go with It" -- tells People she can't wait to "truly show the world my creative ability ... while playing ... different characters."

Montag's getting the ball rolling with a script she wrote herself -- in which she plays a lifeguard who saves a town from a shark attack using her giant "3-D boobs."

Or, in her case, 3-DDD.