Shaquille O'Neal is ready to move out of his incredible 3-acre Orlando mega-mansion ... and it could all be yours if you've got $28 MILLION floating around.

Shaq's pad is famous and awesome ... 31,000 square feet with 12 bedrooms and a buttload of bathrooms.

Not to mention ... a legendary "Shaq Center" athletic facility that is made up of a custom 6,000 square foot basketball court (with bleachers) ... where the NBA star once put Harvey Levin on his ass!!

The estate also boasts the "Shaq-apulco" outdoor area ... complete with a 95-foot long swimming pool and a rock waterfall, according to The Wall Street Journal. Obviously, he's got a hot tub, swim-up bar, walk-in humidor and wine cellar too.

Our sources say these days Shaq's spending most of his time in Atlanta and L.A. -- where he also has Shaq-sized mansions -- so it just didn't make sense to keep the massive Orlando mansion. We're told he plans to buy a smaller place in Tampa, where his mom lives, because that's become home base for the family.

The Orlando crib famously appeared on an episode of "Tanked" -- where Shaq got a custom Shaq Diesel fish tank installed in the home. No word if that stays with buyer or not.

Shaq bought the property in 1993 for $3.95 mil -- but he's done millions of dollars in custom upgrades and expansion.