I have a question concerning to the jurisdiction of the Sanhedrin Gadol. I found in your site that the S.G. can 5 "add to Yerushalayim or the Azaros (of the Mikdash)". What does it mean? What are the Azaros?
The Rambam (in Perush ha'Mishnayos, beginning of Sanhedrin) explains that the reason why the Sanhedrin is necessary in order to add on to Yerushalayim and the Azaros is because when they add to those areas, they are adding Kedushah to the areas, since they were not as Kadosh before (as the Mishnayos say at beginning of Kelim). Only the Sanhedrin (together with the king and the Navi; see Shevous 15a) is empowered to add Kedushah to a place. The Rambam implies that the "Azaros" mentioned in the Mishnah here are the places listed in the beginning of Kelim which have increasing levels of Kedushah. Those places are Har ha'Bayis, the Cheil, the Ezras Nashim, the Ezras Yisrael, the Ezras Kohanim, the area between the Ulam and the Mizbe'ach, and the Heichal.
See the Rashash there, who points out that the Gemara (Zevachim 33a) derives from the verse, "ha'Kol bi'Chsav mi'Yad Hash-m, Alai Hiskil" (Divrei ha'Yamim I 28:19), that the Beis ha'Mikdash and all of its components were built according to the prophecy giving to Shlomo. How, then, is it possible to add on to it, even with the Sanhedrin? The Rashash cites the Gemara later in Zevachim (62a) that states that it was permitted to add to the width of the Mizbe'ach in the times of Ezra, since they found a hint in the Torah permitting such an extension. The Margoliyos ha'Yam cites Tosfos in Zevachim (33a, DH v'Lei'aved) that this applies to the other places as well; whenever a hint is found in the Torah, it is permitted to add to them.
(The Rashash is perplexed, though, why only the Azaros are mentioned, and not Har ha'Bayis, as placed to which the Sanhedrin may add. The simple answer would seem that it is not possible to add to Har ha'Bayis, since the entire mountain is already Kadosh, and whatever they would add would have to be in the adjacent valley and would not be part of the mountain. Consequently, it would not be part of "Har" ha'Bayis. The Rambam (Hilchos Beis ha'Bechirah 6:10) implies even further that it is not possible to add even to the Azarah beyond the limits of Har ha'Bayis. The Margoliyos ha'Yam writes that the word "Azarah" refers also to Har ha'Bayis, as the Tosfos Yom Tov writes (with regard to a different subject) in Sotah 3:4.)