What type of license do i need to drive a 30' box truck for commercial use?

The length of the truck means nothing. What matters is the nature of the use, and the Gross Vehicle Weight Rating of the truck.

If the truck has a Gross Vehicle Weight Rating of 26,000 lbs. or less - regardless of length - is not hauling hazardous materials, and is not a bus designed to transport more than 15 persons (including the driver), you can drive it with whatever the standard license is for your state.

If the truck is under 26,000 lbs. and is either hauling a quantity of hazardous materials which requires placarding, or is a bus designed to transport more than 15 persons (including the driver), then a Class C CDL is required, along with the corresponding endorsements (hazardous materials, passenger, school bus, etc.).

If the truck has a Gross Vehicle Weight Rating in excess of 26,000 lbs., and does not fall into an exempt category, a Class B CDL is required.