what are the 3 most important features in a synagogue?

i really would like to know! help

Roof, walls and the all important floor.

Barnes T (banned again) has said it all really,

I am not Jewish, but I know all synagogues have a Torah scroll, Menorah, and a Shofar.

The Torah, the Torah, and the Torah!
(However, you will also find a Ner Tamid, eternal light, in synagogues.)
.

1 - The Ark where the Torah Scrolls are kept.
2 - The Ner Tamid - the light that reminds us of the light that always burned inside the Temple.
3 - The Bimah, the podium on which the Torah is placed when it is read.
4 - The Amurd - where the leader stands in Orthodox Synagogues during services.

The word synagogue means "meeting place." In ancient times, the only things a synagogue needed was a Torah and people, and that remains true today.

1. The Torah, kept in an Ark.
2. Prayer books, so people know what to say.
3. A Minyan (quorum of 10 men required for prayer, at least in Orthodoxy.)
4. A Chazan, or prayer leader.
5. A Rabbi - not critical, but really useful.
6. A Gabbi - the person who takes care of all the logistics.

(The same person can be the Chazan, Rabbi, and Gabbai, and he counts for a Minyan.)

And yeah, a physical structure.

I get the feeling this wasn't exactly what you were looking for, but anyplace where Jews pray has sanctity - there are no real critical features.

The 3 features that every Shula has, despite the fact that they are not necessary for the place to be called a synagogue, have already been listed by Aryeh M.

(BTW, in #4 he means "Amud," pronounced Ah-mood, not Amurd.)

Wikipedia for more - http://en.wikipedia.org/wiki/Synagogue