Farm structure depreciation

Trying to determine the depreciation term and rate for a farm "structure." 

 

It is a roof over a feed lot for beef cattle. No walls, just two pillars and a roof to shed rain and snow away from the livestock. 

 

The feeder stanchions and cement were depreciated at 7 years at 150% DB but not sure if I can use that same for this.

 

Any suggestions?

 

Thanks.