Investors & landlords

Thanks.  This is very helpful.  I have a similar situation.  However, I'm wondering how to get my original land value.  I know my original price for my rental was $149,000 15 years ago.  Can I make my own assessment based on percentage of land value in my area?  Do I use the latest town assessment for the property and come up with a percentage of land/asset? 

 Please advise.