I had a single player world set up at home and my 2 roomates asked me to open it to Lan so we could play together. No, problem that sounded awesome!

I had everything pretty much sectioned off for my little village I was creating and told them my plans for what I was doing and where everything was going. I told them that X area nearby is free and that if they wished to build anything to go for it over in that area and they could connect it to my road/rail system too.

Both roomates did that until, roomate "A" got bored with her shitty dirt hut and started building somewhere else and kept making these monstrosities everywhere but I didn't care because they were outside my gates… until they weren't. She keeps trying to "help" by building my planned things before I get to them. I have told her to stop, I told her the only reason I play is to build so when she builds what I plan on building it literally makes the game unplayable for me. I have destroyed her creations inside my walls and tried to find a way to put protections up like online servers but I don't think I can on single player.

roomate "B" is fun to play with so I always open up to LAN and roomate "A" joins with him. I think roomate "A" understands that she is pissing me off but doesn't grasp that her "help" is what is causing it. (English is a 2nd language to her), she has stopped building ugly things and then started copying tutorials from youtube to "help" me and I keep telling her I do not want her to build in my walls. I think that may have started to sink in but now she just puts random things in places. She keeps putting pressure plates in front of my doors so they auto open/close… keeps putting enchanting tables everywhere, like 1 in each building and the same for anvils behind every building, and nether portals all over the place (mostly outside my walls but it is still annoying)

I honestly don't think she is trying to grief me and I feel like I have been quite direct and even a little mean, roomate "B" gets it and he tries to curb her enthusiastic "help" but also thinks it is hilarious. She never messes with his builds, not sure why.