Quads and hams on back-to-back days? Any real leg exercise (read: squat or deadlift) is going to involve both muscle groups. If you want a 4-day split, you could try legs,back,chest/shoulder,arms; upper/lower/upper/lower; etc. There are a million ways to skin a cat.
If you are unsure of yourself, try an established program like 5/3/1. Also, CT wrote an article a while back called "How to design a damn good program" that you can probably search for, and will give a wide array of choices for you to decide yourself. It's a bit old but what worked then will still work now.