1.  One who did not build a Succah either by accident or intentionally, he may build one on Chol Hamoed (חול המועד) even as late as the end of the seventh day.  Similarly, he is able to exit from this Succah and to stay in another one. 

2.  One fulfills his obligation with a borrowed Succah.  Similarly, one fulfills his obligation if the Succah is owned by a partnership. 

3.  A stolen Succah is valid to fulfill the commandment of Succot.  How is this?  Suppose one overpowered his friend and forced him out from his Succah.  Then one stole the Succah and stayed in it {1} then he does fulfill his obligation; for land can not be stolen {2}.  [However, it is preferred (לכתחלה) for one to not dwell in his friend's Succah without his consent and surely to steal it.  Similarly, it is preferred (לכתחלה) for one to not build a Succah on someone else's land without their knowledge.  The same applies to public land.  But according to the letter of the law (בדיעבד), one does fulfill his obligation in such cases.  Similarly, a Jew should not gather the Sechach by himself but rather buy it from Gentiles since any stolen thing one should not build a Succah from it according to the preferred way of doing the commandment (לכתחלה)].  If one stole wood and built a Succah from this wood, even if he did not join the planks or change the material at all he fulfills his obligation.  The Rabbis made a decree that the owner of the wood is entitled to only the value of the wood.  If one stole a Succah that was built on top of a boat or on top of a wagon and stays in it, one does not fulfill his obligation.  [Similarly, if Reuven built a Succah on Simeon's land and then Simeon overpowered Reuven and stole his Succah that is sitting on Simeon's land, he does not fulfill his obligation.  Because here this Rabbinical decree does not apply since Simeon did not put any effort into it and did not take it out at all. {3}]
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{1} He occupied anther's Succah in its original place.
{2} Anything attached to the land is considered like land.  Hence, the Succah is considered like land.  Land always belongs to the original owners. So when one drives someone else out of his Succah and occupies it, he does not technically steal the Succah since the land can not be stolen in such a case according to Jewish law. 
{3} M.B.  This case is different then the case where one simply stole a Succah on someone else's land, since over there it is considered like one is stealing the person's land that the Succah is on and land can not be stolen.  Here, since the land belongs to the one who stole the Succah it is considered like he stole the Succah alone which is identical to the case where one stole the wood for the Succah.  But unlike there where the Rabbis made a decree in the thief's favor since he carried the wood, here there is no such decree since the thief didn't do any effort. 
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ShulchanArach.com
Translated by Dr. Jay Dinovitser 11/2009
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