Ohalos 18:10-Negaim 1:1
Ten places aren’t considered non-Jewish dwellings: Arab tents, huts, triangular tents, sheds, summer shelters, gatehouses, the open areas of a courtyard, bathhouses, armories and the places where legions camp.
The signs of negaim (a form of impurity) are two that are four. Baheres is bright like snow; next to it is like the plaster used in the Temple. S’eis is like the skin of an egg; next to it is like white wool; this is the opinion of Rabbi Meir. The Sages say that s’eis is like white wool and next to it is like the skin of an egg.