Maybe they should have included a how-to chapter on plagiarism.

The British brothers behind “The Dangerous Book for Boys” were slapped with a copyright suit yesterday over their best seller’s instructions for building a tree house.

Husband-and-wife writers David and Jeanie Stiles — whose Web site calls them “America’s First Couple of Do-It-Yourself Building Projects” — claim Conn and Hal Iggulden copied plans and pictures from their previously published “The Tree House Book” and “Tree Houses You Can Actually Build.”

The Manhattan federal court suit seeks unspecified damages and destruction of all remaining copies of the book.

Conn Iggulden did not return a call for comment and a spokeswoman for publisher HarperCollins declined to comment.