Benji Madden hired a remodeling crew to overhaul the house where he and Cameron Diaz live, but after what he call shoddy, overpriced work ... the rock star is suing.
The Good Charlotte member says he made a deal with Ryan Silverman and The Wooden Palate in Spring 2015 to remodel his spare bedroom, kitchen, laundry room, deck and a man cave.
According to the docs ... workers finished the project in October 2016 -- at which point Madden had forked over $478,509 -- but he said the job "was done improperly and would have to be redone" ... especially the man cave.
In the suit, Benji says custom built doors for the wine cellar had to be repaired, along with other defects, to the tune of an extra $78k. All in all, Madden wants more than $500k back in damages and a big refund ... plus his legal fees.