I agree with AutoBahn. It isn't a problem if they save your build just to build onto it or play with it, but it's bad if they're taking credit for making it entirely. There isn't such a thing as "build stealing", the proper term would be taking credit for something you didn't do.
I wouldn't care if he had just used it but gave credit, but he actually said I stole it from him just to make a scene and just to try and justify what he did by making people on the server think I stole it from him, people even helped me build, Fun Girl, Sockratis and Scnidcate the Gamer (I don't think I spelled that right) all helped me make that map, I had more than that, I just couldn't name all of them. If you asked them they would say yes, because I made the school and house right in front of Fun Girl, I'm sorry I didn't take a screen shot, because the stuff he said was ridiculous.