If one roofs his succah with spits or bed boards, if the space between them is equal to themselves, it is valid.  If one hollowed out a haystack to make a succah inside it, it is not a succah.

If one suspends the walls from above downwards, if [they are] three handbreadths above the ground, it is invalid; from below upwards, if it reaches a height of ten handbreadths from the ground, it is valid.  R’ Yose says: Just as from below upwards ten handbreadths [suffice], so from above downwards ten handbreadths [suffice].  If one moved the s’chach three handbreadths away from the walls, it is invalid.