I am going to buy a SS or Z28 camaro soon and i am just curious whats the gas mileage like and do u use premium gas? Or what is the best octane for it? is it 89or higher

 

If it is a 4th gen car, the car is designed to perform best with premium gas, 92+ octane. But you can run it on regular if you don't mind losing performance of fuel mileage. You will be burning more of the cheaper gas, and the car won't perform as good at it could.

 

so the middle grade which is the plus grade , is that ok for a camaro SS or Z28 . Its going to be 2000-2002

 

Read the label on the pump, if the Octane number is 92 or greater (except in high altitude locations) it is premium fuel. The LS1 was designed for 92+ octane fuel (premium), but as I said, it will even run on 87 Octane (regular), but it will have less power and burn more gas. But, hey, you can use whatever you want, but don't complain later.
By the way, midgrade (89 Octane) is a rip off, you pay 10C more for 2 Octane points, but for 20C more you get 93 Octane, which is 6 points more.
If you are going out to buy a high power V8, why are you concerned with fuel price? These cars were designed for power, not economy. If you want a nice car that is also economical, get a V6 model. The 3.8s are not slouches either.