Valuation for Depreciation - Property was purchased under value

I have purchased a property for $10,000 when in actuality the property is worth over $250,000.  How do I figure out the land vs. building value for depreciation on my taxes?  There is not assessment because the property was owned by non-profit before purchase. I understand I can only depreciation the building value but how do calculate that portion of the $10k?  The assessor will assess it this year because it will not be under the non-profit ownership anymore but that figure will be far more than I paid.