かみがながいです

To describe someone who has long hair one could say:

トムさんのかみはながいです。　　　Tom's hair is long.

However, it is more natural in Japanese to say:

トムさんはかみがながいです。　　　Tom has long hair (or As for Tom, he has long hair.)

This not only applies to hair length, but to most descriptions of a person's physical attributes.

A さん は　[physical attribute] が　[description of attribute]