Intermission: Notes on いる, ある, である, and っす
要る いる "need" is a different word than いる "exist" and conjugates differently.
ある used to have "real" negative forms (あらず, あらぬ), but they have been entirely replaced with ない. This is the same process that gave us go -> went in english.
Note that some dialects of japanese sometimes use あらへん as a negative of ある, and you will definitely run into あらへん in entertainment media. へん can substitute for ない in general in these dialects.
ある's imperative is あれ, but it's not really used that often, and it conflicts with an unrelated word we haven't introduced yet.
である is appropriate for ceremonies, archaic things, and pretentious things. If someone starts rolling off tons of である, they're not being formal, they're being histrionic. であります is even better.
The etymology of です itself is not known, but the two leading ideas (at the time of writing) are that it's a contraction of でございます or であります.