Final answer:
The subject of the riddle is angles, which are present in both the architecture of houses and the structure of polygons and quadrilaterals.
Step-by-step explanation:
The subject of your riddle is angles. You mentioned that this subject is found in every house in every room, as well as in polygons and quadrilaterals. Angles are indeed found in the corners of rooms in houses as well as being integral to the structure of polygons and quadrilaterals, which are shapes with three or more sides and corners where two sides meet, respectively.