I listened to CD material that was done by experienced people about tax liens. 

Don't bother blaming the guru or the course - the gurus aren't qualified educators, and the course material has not been vetted by educators.

Look at finishes, quality of materials, lot sizes, house size, age, etc.

I've been checking out articles, forums, and educational materials for the last month or so.

If you're really doing that large of a scale, I imagine you have a warehouse where you store materials, right?  

Don't have much to materially add here, but @Jay Hinrichs is right.

What material would you use to fill/fix those holes?

Some advice:Hacking a house you lease or have an option on doesn't give you the authority to make improvements, you may have building code issues and the owner or contractor will need to pull permits.It was mentioned you do that at your own financial risk.Since a Realtor is involved, they may very well advise (and rightly so) for the owner not to allow improvements made from a handyman investor, they will be concerned about the quality of work and so will any lender and appraiser.Contact the insurance agent, most policies allow small improvements to be covered along with liability (not workmen's comp) but generally materials on site will not be covered.

As materialism continues to grow, we accumulate so much stuff we don't need.

Does it have a regular pitched roof or a metal one?