Need help Calculating ARV

[Chris Marte]

Hello everyone, I'm having difficulty when it comes to calculating ARV. I have a good sense of what goes into it (I read J Scott's Guide to Estimating ARV), however I'm having trouble on determining the adjustment values for say an extra bedroom or bath or age of building or cost of porch/deck.

Is there a resource you guys are using to determine these values? I've read it's not always good to use PPSF. 

Are you getting guidance from a property manager or contractor?

Thanks!

Chris