American Chopper

The guys from "American Choppers" got major props for creating a wheelchair-accessible motorcycle -- only problem is they allegedly stole the concept from a disabled biker, and cut the poor guy out of the deal.

Christ Tavantzis -- who suffers from polio -- claims he patented the modified 3-wheeler and pitched it to 'AC' stars Mike and Paul Teutul Jr. at a bike show in 2008.

Now Tavantzis is suing the Tuetul bros because he says they went ahead and built their own version of his trike -- without him -- and then unveiled it at a charity event for the Chris and Dana Reeves Foundation ... where they were lauded for the creation.

In his suit, Tavantzis says it's bad enough polio has taken away his physical abilities -- but now he has to fight to protect his thoughts and ideas too. He's suing for fraud, conspiracy, and discrimination against people with disabilities.

Junior tells TMZ, "It's always sad when a father doesn't come to his own son's wedding, but I still love him, and the truth of the matter is it was an absolutely perfect day and I wouldn't have changed anything."

As we previously reported, the two Pauls haven't been on good terms in a while ... after they clashed over their motorcycle business.

We reached out to Paul Sr. -- but the big mustache refused to comment.

Junior and his bride Rachael married at Bonnet Island Estate in Bonnet Island, NJ. Crazy wedding details included: $28,000 in flower arrangements, a six-tier pink velvet cake with lemon buttercream that featured handmade sugar flowers to match the floral design, and a post-ceremony butterfly release under an arched trellis garden while the strings played "Here Comes the Sun."

We're told the man -- a construction worker not employed by Paul Jr. Designs -- was working on the roof when the accident occurred.

The Orange County Sheriff's Office confirmed that cops are still on scene. We're told someone at the shop called 911 around 8:30 AM to report that someone "fell through the roof."

We're told none of the regular shop employees were inside the building at the time.

TMZ has learned Paul Teutul Jr. is starting a competing shop to go head-to-head with his dad's Orange County Choppers shop.

But here's the catch -- Junior has recruited a bunch of disgruntled employees who left his dad's place ... including his brother Mikey Teutul and friends Vinnie DiMartino, Robert "Nub" Collard and Joe Puliafico.