Remeasuring added square footage after rehab?

[Steven Barr]

I just rehabbed a house and I have the appraiser coming out in a few days….

There is some additional square footage now, but I am unsure how to officially record this for the appraiser to take into account 

Is this something that I can measure myself and just tell the appraiser? Or does a certified professional have to come do it? If so, who would that certified professional be?

thanks guys!