[chryuop]

That is called Ellyptical construction (or something like that). It exist when a big part of the phrase is already known and thus it is cut off and the です part will substitute it. But I don't think you can use it from "scratch", without having introduced the topic previously.
I will try to do an example.
レストランで。
ボブ：僕はてんぶらを食べたい。お前は？
ジム：僕はすしだ。
Literally it means I want to eat tenpura and you? The answer doesn't mean "I am sushi", but it means I want to eat some sushi. In this form what the phrase actually should be is: 僕の食べたいことはすしだ (the thing I want to eat, is sushi).
As you can understand if I come up to you and all of a sudden I start saying 僕はすしだ it really makes no sense and you would call a shrink for me. It all has to do with what was said previously.

(Always wait for a native to confirm this, I will never get tired of saying it).