Is that common? 

In that case the error is obvious, but they still need to notify everyone immediately of the mistake.

Expecting about 20,000 sqft of construction (units and common areas).Related info:Type:Garden-style2-levels with mix of 2 Bed/2Bath and 1 Bed/1Bath unitsMid-grade constructionSite info:Flat land, no major grading work is neededUtilities are yet to be connected (the site is in a developed neighborhood with good road access and utilities at curb side)Expansive soil (known for this region)Thanks!

Ofc, I am still doing my own due diligence hence finding out other common inspections in Alabama. 

Is this common?

Your friend speaks in hyperbole . . . they mean to say that it is most common to buy off market properties cash. 

Here's the steps you should take to learn the basics of estimating rehab costs:#1 Read 'The Book on Estimating Rehab Costs'First, you need to build a foundational knowledge of construction, inspecting properties and putting together a detailed SOW.JScott's 'The Book on Estimating Rehab Costs' is a great resource for new rehabbers to learn how to Estimate Repair Costs on 25 common rehab repairs.https://www.biggerpockets.com/store/the-complete-g...#2 Explore Lowes and Home Depot to Learn About Material PricingTake a tour through Lowes and Home Depot (or their websites) and look at finishes materials and fixtures that you will consider using in your rehab projects.

Verbal testimony is very common in court, so of course this is useful. 

As appraisers rarely make that kind of error I would hazard a guess that the sq ft is below grade and included in below grade sq footage on the report.

I also get ones without a string since that is one of the most common pieces that gets broken.7.