Neighbor built over property line.

[Richard D.]

I am currently looking at a vacant lot, where it appears that the neighbor has built 6 inches to two feet over the property line (30 feet deep). I won't be absolutely sure until I can get to the county clerks office for plat maps. 

 Since the structure is affixed to their main house, I don't think moving it would be a viable option for them. They are also in the process of rehabbing the home. It's vacant, and according to the other neighbor on the other side, the home has been an on going project for the guy. I have no idea if they even got the permits to build this portion at all.

 How would you approach the neighbor if they are over? Would you offer to rent the section of the property to them? Would you sell that section to them, and have them re-plat the two properties? Would you just threaten to tear it down, to get their attention to discuss the oversight/building error?

With the building over it would hamper a potential exit strategy for me. It also has caused the fence to be overgrown by 2-3 trees, which would need to be removed, unless they bought that section of the lot. 

Any advice on how to handle the issue with the neighbor would be greatly appreciated, thank you in advance.