Negaim 12:1

All houses can contract nega impurity except for those owned by non-Jews. If one bought a nega-infected house from a non-Jew, it must be inspected as at the outset. A round or triangular house, or a house built on a ship, a raft or on four beams (i.e., suspended above the ground), is not susceptible to nega impurity. If a house has four-sides, then it’s susceptible to nega impurity even if it’s built on four pillars.

Negaim 12:2

If one side of a house is overlaid with marble, rock, bricks or earth, it is insusceptible to nega impurity. If a house contained no stones, wood or earth when a nega appeared and stones, wood and earth were subsequently brought into it, the house remains ritually clean. Similarly, if a garment contained no woven part three fingerbreadths square when a nega appeared in it and a piece of cloth three fingerbreadths square was subsequently woven into it, it remains ritually clean. A house is not susceptible to nega impurity unless it contains stones, wood and earth.