Assuming the recently discovered lava tube is exactly what scientists think it might be, and assuming you could build 2 walls and a door in side the lava tube, and assuming you filled it with a breathable atmosphere...
How livable would such a place be?
Would people need to wear protective clothing? Would the air pressure blow the roof off? Would the natural gravity be high enough to support life? Would the enclosure retain the right amount of heat to sustain a livable temperature? Etc. (These are sample questions, not necessarily relevant to the answer)
In general, would the lunar lava tube, with nothing more than 2 new walls, and a breathable air pressure be able to sustain a livable environment?