Basic jungle starting items I don't really mix it up a bit yet.

I start with Rod of Ages because Diana is really heavily mana hungry and it allows me to give my blue to mid, it also gives me some extra hp and ap. I then rush rabbadons because it gives me high damage outburst for ganks. I then get a rylais for ganks to slow the movement with my already op slow knockup it makes a killer combo, by then if you are playing right they have a hard focus on you with your short cooldowns making zhonyas really good for when you either have a heavy focus or if you are going one on one and need a quick second to get your Q or W back. I then get abyssal scepter for the magic resist and by now they probably have magic resit giving you a little bonus on penetrating that magic resist. I finish with a g/a for the resistance and the passive of course.

Some people prefer to rush W instead of Q maxing it first but for me I find it better for ganks for the extra cooldown on your Q to allow to get another 1 or 2 lunar rushes in. I also find that you will land your Q a lot more times than you will use your W and for that I simply just stick to upgrading Q first.

Some people prefer going more into tankiness and taking away the 5 last points or more and add to resistance/bonus hp but this is just my preference because for low levels on Diana I like the ability to burst really high in my ganks.

I like having my armor and magic resist for obvious reasons, armor for jungling low levels it helps so you do not have to recall, and as a jungler your build normally is more towards armor so the magic resist really helps considering how APCs are normally really the most powerful end game. I use scaling ap instead of base ap because 4.5 ap at lvl 1 really isn't worth it.