Suka page 4 and Eruvin page 89b. there is what looks like a contradiction in law. In Suka Rav Nachman said we say see the walls as extending upwards in the case of a four poles put on the sides of a roof. And the Rambam decided this as the law as he writes one stuck four poles on the corners of the roof, and put sa covering of leaves over them, the suka is valid, and we see the lower walls as if they extended upwards until the corners of the covering of leaves. However in Eruvin, the sages said the when you have joining roof tops that they are all considered as one domain. The Gemara says that is the law. Yet there we do not say the walls of the buildings under the joined roof tops are considered to extend upwards. The difference I think is clear and also hinted at in Tosphot. In the case of the roof tops, the lower walls of the buildings are completely obscured by the roof tops and they are definitely not seen. But we the suka the wall of the house is at least seen from the outside._______________________________________________There is what looks like a contradiction in law סוכה page 4 and עירובין page 89b. In סוכה,רב נחמן said we say see the walls as extending upwards in the case of a four poles put on the sides of a roof. And the רמב''ם decided this as the law as he writes one stuck four poles on the corners of the roof, and put a covering of leaves over them, the סוכה is valid, and we see the lower walls as if they extended upwards until the corners of the covering of leaves (סיכוך) . However in עירובין, the sages said the when you have joining roof tops that they are all considered as one domain. The גמרא says that is the law. Yet there we do not say the walls of the buildings under the joined roof tops are considered to extend upwards. The difference I think is clear and also hinted at in תוספות. In the case of the roof tops, the lower walls of the buildings are completely obscured by the roof tops and they are definitely not seen. But we the סוכה the wall of the house is at least seen from the outside.