The legal question is whether you have any responsibility for the builder. The answer is "probably not". However, as has been pointed out, the heirs can drag you into court and you can be in the right, but it is still very costly to defend yourself. So, if you are uncomfortable with the situation, you should put an end to it. It's that simple. Dont' be a wimp about it. Tell they guy you are uncomfortable with the situation and give him a date when you expect him to be out of your hangar.

It's not an unusual situation for a builder to think they have found a home in someone's hangar, but the hangar owner figures out the builder does poor quality work, or may have had intentions of knocking out a lot of work, but accomplishes very little other than to take up your time and hangar space. I've had that situation, and as much as I like helping builders, I have had to give them a drop dead date to find another storage facility and throw them out of my hangar.