This build is a work in progress still and will be updated throughout S7 but for now, this is the best I could come up with. It works very well in game and anyone who uses it should be pretty happy with Yi.

The whole point of this build was obviously life steal. With it [A lot of it (at least over 20%)] it will be hard to kill Yi unless hard (long) cc is cast on him (Such as Morgana's Q). The fervor will give you extra damage, good for 1v1s or 2v1's or anything like that. Also for long team fights. Since he has a huge amount of attack speed the life steal comes quickly.