Calculating Building Basis -Appraisal vs. Property Tax Assessment

[Kate McClinton]

Is it permissible to use the allocation of building to land from the county property tax assessment instead of an appraisal?  My CPA said we had to use the appraisal allocation as it was the most accurate, yet the property tax assessment allocates a higher % for the building (which would be more favorable).  Thanks so much for your help!