One of the biggest things I have ever seen on the road was a two-story Bellemonte Victorian mansion built in 1817 that was moved about two miles from where it was built to it current location on the college campus where my wife teaches. It was remodeled/restored and serves as guest quarters for important visitors.
The largest thing I have ever seen moved in part was the Cape Hatteras Lighthouse. It was moved in 5 foot increments over the course of 23 days for a total of 2900 feet. I actually saw it move about 25 feet on one of my visits to the operation. Here is a video that explains the move and how it was accomplished. It was one of the most amazing things I have ever seen. I spent a lot of time surf fishing at Cape Hatteras in the shadow of the lighthouse.