Tommy Lee -- SUED Over Roller Coaster Drum Stunt

The man who claims he invented Tommy Lee's awesome roller coaster drum solo thing has kept his word -- officially following through on a promise to SUE the drummer ... for allegedly jacking his design.

L.A. based engineer Scott King filed the lawsuit in L.A. County Superior Court, claiming he approached Lee back in 1991 with an initial design for a drum-roller coaster for his concerts ... and Lee jacked it for Motley Crue's 2011 tour.

Now King is suing Lee for stealing his idea -- demanding at least $400,000 in damages.

TMZ broke the story ... King sent Lee a warning shot last month -- in the form of a legal letter -- promising to sue if Lee didn't pay up. Well, Lee didn't pay up.