Minecraft Building Ideas For Survival?

Make a copy of your house or apartment( if you live in one ).

I usually don't do a lot of farming, but I DO usually have a gigantic tree farm, like underground tree forest.

Farming shrooms automatically is cool, although you probably wouldn't find that much of a challenge.
You might not be crazy about farming hostile mobs, but if you can build a witch farm you get a lot of free cool potion ingredients and stuff.

Also, huge piston gates and drawbridges are cool, just piston structures in general, and if you can build a working elevator in SMP… I think that's the gold standard for houses in minecraft, an actual working practical piston elevator in multiplayer, that works 99.9% of the time, and doesn't insta-kill you the other 0.1% Post that on the youtubes if you get it working.

On our server, I had everything else, the little base at the sky limit with an observation tower, but I could never get the elevator to work even close to consistently, couldn't find anything better on youtube.